Just got a new Light and need help

[jdogrulz]

87° and 54%? That's very harsh conditions for cannabis.

VPD is a very good way to express combinations of temperature and humidity. This page is a good explanation of VPD.

VPD is akin to "feels like" for humans. At 87 and 51, your plants are functioning in a desert-like environment.

In veg, cannabis grows best when VPD is 1.0 while VPD in flower should range from 1.2 to 1.5 ( prefer 1.2 or 1.3). Check the intersection of 87 and 54 and your plant is working in a VPD of 1.7±.

To function in a hot and dry environment like that, your plants have to throw off a significant amount of water. Like humans, plants can be described as "bags of water" and when the air is hot and dry, water will flow from that a bag of water to the outside air. That's because there's not a lot of water in the air but there is a lot of water in the plant <== that means that the "deficit" is high and, in nature, everything tends to move from high to low.

With all that water leaving the plant, the roots have to take up a lot more water than normal and when plants take up a lot more water than normal they also take up a lot more nutrients than normal.

In terms of VPD, your plants will do better growing in an environment that is about 10° lower.

The other reason to lower the temperature is that at 87° you're "decimating" your cannabinoids The word "decimate" is a paraphrase of how the loss of cannabinoids was described when temperature of the flower tops of cannabis plants exceeds 78°.

Mitch Westmoreland, a cannabis researched studying under Bruce Bugbee, did a video on growing hemp about three years ago and he mentioned that…

[searches for notes and finds them]

I've grown my plants in the low to mid 80's and, while some of the yields have been prodigious, they haven't had the kick that I associated with premium bud that I've bought from resellers here in CA. In response to the Westmoreland videos, I'm changing my growing processes and am replacing my flower light so I can provide my plants with 1100µmol± as well as keeping the tops of the flowers <78° in flower.

Below are the notes I took on the Westmoreland video on hemp.

Does Hemp Need Extra Water and Fertilizer?
Mitch Westmoreland


Plants grown at 73 and 84 degrees. Plants at 84 were taller but colas were smaller in girth.

At 84 little but taller, a bit more vegetative biomass. Yield wasn't all that affected by the increase tempearature. At 84°, cannabanoids were roughly 1/2 of what they were at cooler temperatures.

Suggest that the optimum is between 70 and 80.

Fertilizer
You've probably come across hundreds of companies promising to boost yield. They "lack a theoretical basis" and you'll probably end up just throwing away money and excess nutrients that will end up polluting our nice rivers.

We recomend that you fertilize it just as you would tomatoes. This is a good comparison there's nothing particularly special about hemp.

One of the big claims that you'll see coming out out of the cannabis industry is that high phosphorus will increase yield and will increase cannabanoid content. We've tested this.

We look at a range of phosporus treatments ranging from borderline deficient to excessive. We found no significan difference, especially as we move toward the rates recommended by the cannabis industry. This has implications because phosporhus is a potent pollutant in our environment.

What we're trying to do is get growers to use as little P as we can while still getting a good crop.

Drought stress
In veg - they're very resiliant. Got to the point where they were severely wilted. They recovered so that it seems as if nothing happened. Hard to see which one's were stressed and while ones were well watered.

In flower - yellowing and dropping of leaves and reduction in yield. CBD and THC does not make production increase.

Temperature - yield increased slightly. CBD and THC plummeted - "cut in half basically". We don't have a good explanation for this right now. We're going to ssee if we can reproduce this and see if we can come up with an explanation for what's going on."

Per my notes, above, high temps will result in a signficant loss of THC and CBD (he doesn't mention terpenes here). Westmoreland continued his research in this area and, in early 2024, released two videos in which he discussed some of the aspect of the work that he had presented for his PhD thesis.

This graphic, the growth rate which is substantiated in other published research, it why I recommend keeping light levels as high as the plant will tolerate. Other research shows that the result is not quite linear but the research indicates a direct cause/effect relationship between increased light levels and crop yield, assuming that light is the limiting factor.

My advice, read up on VPD (you need an IR thermometer to get your leaf surface temperature), drop your tent temp and LST, and adjust your RH so that your VPD is 1.2. That won't bring back the dead tissue in the leaves but it will deduce the very high transpiration rates and that will help resolve the nutrient issue that you're looking at

Sorry but I dont agree with the higher RH levels that you are talking about, or maybe I missunderstood?

When you google what the best RH is for cannabis during the flowering stage, you will find just about every site says 40% to 55%, and that includes the Big Seed Banks, Spider Farmer, and all the rest of the big wigs that know what they are talking about.

And myself included, this is not my first grow, just the DWC is first time. I have had others that all went well at 50% to 55% during flowering. I use a good balance range between 60 and 70% for VEG, and of course 80% to 90% for Germination.

 

[Sativa1970]

Couple things can cause PH drift.

False start; You need to set the PH and give it time to settle between mixing steps. Everything you add effects PH but the reaction is not completed in an instant. The more you add the longer the reaction takes to settle. Wait 15 minutes between each step to get your PH reading.

Nutrient fall out; If your PH is too far out of range nutrients will fall out of suspension. Since most nutrients are acidic, when they fall out, PH rises, more fall,, so on. You will see a white powder on the walls and bottom of res.

NPK ratio imbalance; If your ratio of NPK is mismatched to what the plant takes up you could be, for example, in N defalcate and P toxicity at the same time. This causes the PH to drift. The bigger the mismatch the faster and farther it will drift.

Yes your RH% is good but the temperature is wrong so temp Relative to Humidity is wrong. You should be closer to low 70sFht. If you drop the temp it will change the humidity %, relative to temp. Adjusting for correct temp would push you around 80RH. So lower the temp and remove moisture to the low 70s fht and roughly 50%RH.

 

[Sativa1970]

To be clear, your plant will grow and flower at the wrong temp and RH. That isn't the issue. You will loose some yield, terpenes, cannabinoids, risk health and pest issues when it isn't kept in check.

 

[jdogrulz]

Couple things can cause PH drift.

False start; You need to set the PH and give it time to settle between mixing steps. Everything you add effects PH but the reaction is not completed in an instant. The more you add the longer the reaction takes to settle. Wait 15 minutes between each step to get your PH reading.

Nutrient fall out; If your PH is too far out of range nutrients will fall out of suspension. Since most nutrients are acidic, when they fall out, PH rises, more fall,, so on. You will see a white powder on the walls and bottom of res.

NPK ratio imbalance; If your ratio of NPK is mismatched to what the plant takes up you could be, for example, in N defalcate and P toxicity at the same time. This causes the PH to drift. The bigger the mismatch the faster and farther it will drift.

Yes your RH% is good but the temperature is wrong so temp Relative to Humidity is wrong. You should be closer to low 70sFht. If you drop the temp it will change the humidity %, relative to temp. Adjusting for correct temp would push you around 80RH. So lower the temp and remove moisture to the low 70s fht and roughly 50%RH.

So my routine has always been, fill bucket with de-chlor. and airiated tap water (tap water sitting at least 24 hours and with air running through it), then I test the PH, it is usually between 8-9, then I mix the 3 nutes from my TA TriPak and then test ph again. It usually is around 7-7.3. So I use my BioBizz Down and get it to 5.8. And I always stir the meter around for a while to make sure it is going to stay at the last reading. I mean I dont wait 15 mins, but until I dont see the meter moving anymore, or at least it is just moving up and down by 0.01. Thats it, and this has always worked in the past.

The only thing different from my grows from before is the tap water. We have moved since the last grow and this is the first time I have ever had such a high PH in my tap water.

Please let me know if there is anything that I am doing that could maybe be changed. Like I said this has always worked for me before but if I need to do something different becuase of the high ph I am more than willing to give it a try.
Tomorrow will be be the big test. I am anxious to see what the levels are on my DWC. Will be able to see if I am going to have to be doing a lot of tampering with the PH every day.


The Temp is not normal. Normally I have between 75f-81f, but it is extremely hot outside in the last few days so I cant do much about it until this heat wave passes.

thanks again for all the info and help!

 

[jdogrulz]

Well I guess my new tent is not anything to write home about?

Not one comment on all my hard work, and all that after my 6th back OP just 4 weeks ago

Just dont tell my doctor that I am doing all this...LOL

 

[Delps8]

Sorry but I dont agree with the higher RH levels that you are talking about, or maybe I missunderstood?

When you google what the best RH is for cannabis during the flowering stage, you will find just about every site says 40% to 55%, and that includes the Big Seed Banks, Spider Farmer, and all the rest of the big wigs that know what they are talking about.

And myself included, this is not my first grow, just the DWC is first time. I have had others that all went well at 50% to 55% during flowering. I use a good balance range between 60 and 70% for VEG, and of course 80% to 90% for Germination.

I don't see a mention of RH in what I wrote. As best I can tell, the information I provide had to do with vapor pressure deficit but I re-read what I wrote pretty quickly so I might have missed it. The issue is, I really don't think in terms of RH because it's got limited applicability under temperature is taken into account. And then you have both of those values, VPD is an easy way to discuss that part of the growing environment.

If asked a question about what RH to use in flower, I'd answer that 50-60% is generally the RH that's needed to result in a VPD of 1.2 to 1.4. Soon after I started growing, I learned about VPD because it's a better way to understand the growing environment than to speak of temperature and RH seperately.

Check out the link that I provided about VPD. It provides a good explanation.

I've set RH as low as 45% and up to 60% in flower because, based on the temperatures that I have in my grow environment, that's what allows me to have a VPD of 1.2-1.4 (I don't recall hitting 1.5).

My assertion is that, as a result of your temperature and RH, your VPD value is very high and that will tend to drive up transpiration rates which can, in turn, cause problems.

Re. RH for DWC vs soil - can't think of a reason why it would be different. As long as it's a cannabis plant, the numbers you're suggesting are good general numbers.

 

[jdogrulz]

Couple things can cause PH drift.

False start; You need to set the PH and give it time to settle between mixing steps. Everything you add effects PH but the reaction is not completed in an instant. The more you add the longer the reaction takes to settle. Wait 15 minutes between each step to get your PH reading.

Nutrient fall out; If your PH is too far out of range nutrients will fall out of suspension. Since most nutrients are acidic, when they fall out, PH rises, more fall,, so on. You will see a white powder on the walls and bottom of res.

NPK ratio imbalance; If your ratio of NPK is mismatched to what the plant takes up you could be, for example, in N defalcate and P toxicity at the same time. This causes the PH to drift. The bigger the mismatch the faster and farther it will drift.

Yes your RH% is good but the temperature is wrong so temp Relative to Humidity is wrong. You should be closer to low 70sFht. If you drop the temp it will change the humidity %, relative to temp. Adjusting for correct temp would push you around 80RH. So lower the temp and remove moisture to the low 70s fht and roughly 50%RH.

Well I measured the DWC water this morning and sure enough it was back up to 8.5, shit!!! That went from 5.8 up to 8.5!!

Well I have to go adjust.

Also, could someone help me with TDS? I am not used to working with that, the soil always used to take care of that for me.. Right now I am getting 330ppm. My tap water ranges from 190-200.
The TA TriPart has a chart that says it should be between 0.2 - 0.5.
The conversion chart for ppm has a reading for 500ppm and another one for 700ppm and this is where I get mixed up. Is this for Softwater and Hardwater? And is mine considered Hardwater since it has a normal reading of 200?

 

[Sativa1970]

RH is the same effective as reading VPD if your temp is correct. VPD is useful when your temp is out of range. If you adjust your VPD, the temp may be wrong but humidity is correct so fewer variables are off.

You need to correct the PH first. The PH should not be over 8 when adding nutrient. If your current method is add nutes then add 1 tsp of PH down you need to flip it. Rest the water with1tsp PH down, then add nutes. The air flow can effect PH. O2 raises PH and CO2 drops PH. Roots respirate both O2 and/or CO2 into the "soil". We aerate the res to keep these two levels at ambient.

It is also possible the plant is flushing. Roots don't physically suck up water and nutes. They use pressure gradient. Basically everything flows from high concentration to low concentration because of natural balance. A dry root will absorb water from wet soil just like a wet root will send water into dry soil. Same applies to all chemicals. If there is a vary high concentration of N in the res it will flow into the roots. If you then place those roots into a low concentration res the roots will send N into the water until they are balanced. So the plant could be flushing acids into the res when you change it.

PPM is not a universal unit of measure. There are 4 different scales, so always assume someone else PPM number uses a different scale. 500, 640, 700, and 1230 are the scales that all equal to 1EC. Look for one of those numbers printed on the meter. EC is universal. The scale makes no difference if you are using it to read your plant. You are just looking for the change in value. If the value goes up you are over feeding. If it goes down you are under feeding. Trying to match another persons number with a different strain in a different environment is pointless.

On the 3 common scales PPM 200 would be .4 to .5EC. That is not bad at all. Your total EC, starting water + nutrient should = between 1.2 and 2.0 EC. The more, that is in your tap water already, the less nutrient you can add. So if your tap water is .5EC and they say nute A should be .5EC, you should have 1.0EC after adding nute A to your water. Young plants stay closer 1.0EC while established plants can take up to 2.0EC. Under feeding is always better than even a slight over feeding.

There is no defining line for hard/soft water. You may be able to find a water company evaluation showing what is in your water or have it tested. I used strait tap .4EC (180PPM) for a few years with no issues. My water company no longer uses chlorine here so it dropped to .2EC (110PPM). Water report shows it is 80PPM of the 110 is calcium and magnesium. What is in the water is just as important as how much is in it.

 

[Sativa1970]

Forgot to add that when chlorine breaks down in the water it creates free radical O3. This will happen naturally over 48 hours but accelerates when in contact with organic mater like bacteria, algae, or roots. O3 will drive the PH up.

 

[jdogrulz]

RH is the same effective as reading VPD if your temp is correct. VPD is useful when your temp is out of range. If you adjust your VPD, the temp may be wrong but humidity is correct so fewer variables are off.

You need to correct the PH first. The PH should not be over 8 when adding nutrient. If your current method is add nutes then add 1 tsp of PH down you need to flip it. Rest the water with1tsp PH down, then add nutes. The air flow can effect PH. O2 raises PH and CO2 drops PH. Roots respirate both O2 and/or CO2 into the "soil". We aerate the res to keep these two levels at ambient.

It is also possible the plant is flushing. Roots don't physically suck up water and nutes. They use pressure gradient. Basically everything flows from high concentration to low concentration because of natural balance. A dry root will absorb water from wet soil just like a wet root will send water into dry soil. Same applies to all chemicals. If there is a vary high concentration of N in the res it will flow into the roots. If you then place those roots into a low concentration res the roots will send N into the water until they are balanced. So the plant could be flushing acids into the res when you change it.

PPM is not a universal unit of measure. There are 4 different scales, so always assume someone else PPM number uses a different scale. 500, 640, 700, and 1230 are the scales that all equal to 1EC. Look for one of those numbers printed on the meter. EC is universal. The scale makes no difference if you are using it to read your plant. You are just looking for the change in value. If the value goes up you are over feeding. If it goes down you are under feeding. Trying to match another persons number with a different strain in a different environment is pointless.

On the 3 common scales PPM 200 would be .4 to .5EC. That is not bad at all. Your total EC, starting water + nutrient should = between 1.2 and 2.0 EC. The more, that is in your tap water already, the less nutrient you can add. So if your tap water is .5EC and they say nute A should be .5EC, you should have 1.0EC after adding nute A to your water. Young plants stay closer 1.0EC while established plants can take up to 2.0EC. Under feeding is always better than even a slight over feeding.

There is no defining line for hard/soft water. You may be able to find a water company evaluation showing what is in your water or have it tested. I used strait tap .4EC (180PPM) for a few years with no issues. My water company no longer uses chlorine here so it dropped to .2EC (110PPM). Water report shows it is 80PPM of the 110 is calcium and magnesium. What is in the water is just as important as how much is in it.

WOW! Thank you SO MUCH for all that great info, and the explanation is great to, as even a dummy like me can understand it, so thanks again for taking the time to help!

Ok now to some questions, first, my DWC grow just started so as for now there are no roots involved so we can put that out of the equation.
Thank you for correcting my on my procedure, as it seems I was doing it backwards. After your explanation I now understand why. I have corrected the PH and it is now back down to 5.5.

I always de-chlor. ( I don't think it is a real word but sounds good...lol ) my water for at least 24 hrs and I aerate it also.

I am not trying to copy anyone's numbers, I am simply following the charts from my nutes.

 

[Finnicki]

Use the back of your hand at the top of your plant to feel the heat from your lights. You can easily feet if there is too much there. You should barely feel it on your skin.

 

[Delps8]

Use the back of your hand at the top of your plant to feel the heat from your lights. You can easily feet if there is too much there. You should barely feel it on your skin.

That was conventional wisdom when using gas discharge but is not valid for LED grow lights. Modern LED's don't generate any light in the IR spectrum and may not even feel warm to the touch even if they're generating very high levels of light.

 

[Finnicki]

I have two LED’s in my tent and the temp is 80. 60x27x80. Had the door unzipped today for awhile as I blew air from outside the basement ‘fruit cellar’ room into to try and cool it down. I’ve dialed the light intensity back to try and help. RH is in the 40’s. I think the hdwe on back of the LED’s is the source. Turned the exhaust fan speed up one setting as well. I have a new auto as well as a mature plant in tent.

 

[SmokingWings]

may not even feel warm to the touch even if they're generating very high levels of light.

I am running several T5 fixtures and can feel heat on the back of my hand starting about 4 inches away. Not hot but there is heat coming off the tube of diodes. I can touch the front of the tube/lamp and it will be very warm but not feel burning hot. The back of each lamp has a reflector of sorts and that will get hot to the touch.

Plants will react mildly when they grow up close to the lights with the familiar tips and sides of the fingers curling. If the leaves get to within an inch and especially touch the lamp for several hours or longer they will wilt and burn. Not the whole leaf but any part that touched the lamp will show as a cream or white color. The rest of the leaf stays alive. I have to be believe that if the growing tip were to touch that part would die.

When I lower the plant back down to a more normal distance the growth continues as usual but the damaged areas remain. In the photo in msg #8 I can follow the path of the two lamps on the leaves.

 

[Sativa1970]

When I said don't fallow others numbers I was referring to any recommended EC and more specifically PPM. PPM is not a universal scale and only your plant knows the correct EC. Start with the chart recommended ML per L mix and get a reading from your meter. That number on your meter is now the zero point on the scale. Future readings of the res compared to that number will tell you if you need more or less nutrient.

Are you adding a chemical dechlorinate or dechlorinating by aerating it out? Or both?

This is a first run in DWC.. You have new clay balls in the net pot.. Did you clean and PH soak them? You should rinse them well to get all of the red powder off. Then soak them in PH water, changing water as needed to neutralize them. They have a vary high PH strait out of the bag. You can drop a hand full of clay balls into a small container of PH water and watch the PH rise. If this is possibly your problem, place the plant over an empty bucket. Slowly pour PH water through the media. When your catch bucket has close to the same PH as you poured, return it to the res.

You can reuse the clay balls but after each grow you need to clean, rinse and soak them.

 

[jdogrulz]

When I said don't fallow others numbers I was referring to any recommended EC and more specifically PPM. PPM is not a universal scale and only your plant knows the correct EC. Start with the chart recommended ML per L mix and get a reading from your meter. That number on your meter is now the zero point on the scale. Future readings of the res compared to that number will tell you if you need more or less nutrient.

Are you adding a chemical dechlorinate or dechlorinating by aerating it out? Or both?

This is a first run in DWC.. You have new clay balls in the net pot.. Did you clean and PH soak them? You should rinse them well to get all of the red powder off. Then soak them in PH water, changing water as needed to neutralize them. They have a vary high PH strait out of the bag. You can drop a hand full of clay balls into a small container of PH water and watch the PH rise. If this is possibly your problem, place the plant over an empty bucket. Slowly pour PH water through the media. When your catch bucket has close to the same PH as you poured, return it to the res.

You can reuse the clay balls but after each grow you need to clean, rinse and soak them.

I just let my water stand and with aerater, no chems.

Yes I cleaned and put them in PH water afterwards.

Well I am going to have to wait to do anything else as I am in the hospital and waiting to get operated on. I had my spine operated on 4 weeks ago and now the wound has come open and filled my house floor with a lot of blood :-(

So talk to you all later after my OP, take care and thanks again for all the tips, from everyone!

 

[Finnicki]

Get well. They need to use better glue & duct tape to keep those incisions closed.

 

[Sativa1970]

Good luck and get well. My procrastinating left me staring at a celling in traction for 6 months. Take care of yourself. If you have any questions after you get back on your feet we will all be here.

 

[jdogrulz]

Thank you for all the well wishes and kind words!

I made it through the OP and early results are positive. I will be in here for another 2 weeks at least, so we will see what the future brings.

I am going to try and guide my wife through taking care of the ladies, but she is not a green thumb so it will be fun.

Thanks again eveveryone and keep growing big juicy buds!!

 

[bluter]

I am going to try and guide my wife through taking care of the ladies, but she is not a green thumb so it will be fun.

have her post under your username if she has any trouble. we'll make sure she's ok.