Examine just what the meter told you? That it is moist? The only useful thing that meter does is to tell you where the water table is... that lake of stagnant water that exists in the bottom of your container. You need to let that lake fall down to the last inch of the container. This is the ONLY way that oxygen is able to be pulled down to those bottom roots, because of the suction that the top of the lake causes (diaphragm effect) and it is necessary for those roots to periodically see oxygen. If they stay under water the roots have no choice but to try to protect themselves from the flood waters, and they enclose themselves in a protective covering until it dries out. When this happens, a good amount of the root's ability to uptake water and nutrients is shut down, just trying to survive. This lack of nutrition is what these bottom leaves are showing you... the Nitrogen needed by the plant for all the new growth is now lacking because those feeder roots are being compromised, so it is drawing it from the storehouses in those lower leaves.
Your watering every 2nd and 3rd day before the plant is able to use all of that water sitting in there simply raises the level of the water table again, keeping the lower roots under water. While this is harming the lower roots, this is a weed, and being such it has two sets of roots, and the top spreader roots are now taking prominence and are getting most of what the plant needs into the plant. I bet they perk up a bit when they get this watering, but then 12 hours later they are drooping again. You are getting to the point where the only active roots will be the upper ones, and when that happens you will lose all of your lower leaves... it is an ugly process and we need to stop this now so you don't get to that point.
Learn to use the lift method. Lift up a similar sized container filled with dry soil and note its light weight. Now lift your plant. If your human senses can discern that there is water weight in there as compared to the dry pot, it is NOT yet time to water. Let the plant use all of the water in the container before you reward it with more water. This will cause the roots to expand out tremendously between waterings, looking for that water. A healthy plant reaches up toward the light, while these powerful roots develop the water pressure necessary to do such a powerful thing. It will amaze you how a planter that feels so light and obviously is as dry as the Sahara, can hold such a happy plant, but this plant is most happy when it is almost so dry it is to the point of wilting, while a coddled and constantly moist weed will be an unhappy and lazy one with a feeble root system. Weeds need a little bit of adversity to thrive. You must be cruel to be kind... and all that. Don't be afraid to let it dry out. If it takes more than 4 days to get totally dry, give it a little tiny drink, just watering the top roots and no further down than 3 inches... give just enough water to give the top roots a little drink but not add to the water table down below.
Develop a clear wet/dry cycle, where you can see the roots getting stronger with each cycle. At first it will take 5-7 days to drain a container of all the water you can get the soil to hold. As the roots develop, that time between waterings goes down a bit each time, and when the plant can drain every drop in 24-36 hours, it is time to uppot, and start this root building process again.
Check out my watering article for many more thoughts on this process and how it modifies as the plant matures.
