LOL Canna. Sometimes I'm too Schmart for my own damn good and go all kinds of Rube Goldberg. Overthinking things can be a debilitating handicap!
Not being able to rotate plants to even out light, difficulty watering and NOT BEING able to flush effectively are some major downsides to the SCRoG, for sure.
Now I'm on a roll and am going to go on a flushing rant. Many growers think of a flush as something that's good in the last two weeks, or as something to do when things go drastically wrong. Not many grasp the notion that flushing is a way to prevent big problems from happening in the first place. I'm prone to analogies, and I'm going to nauseate anyone who actually reads my drivel with an analogy now.
Someone feeds me breakfast every day. Usually it's the same thing, a big bowl of Total breakfast flakes fortified with eleven different vitamins and minerals. They give me a nice big portion. I don't finish it all. The next day I'm given another nice big portion of Total. The leftover uneaten Total is still in the bowl from the day before. I eat roughly the same amount of Total as I did the day before. The amount of uneaten total in the bowl doubles. The next day I get another big serving of total dumped on top of two days worth of left-over Total... You can, I'm sure, see where we're headed...
When we mix up our nutes and feed plants growing in a container, we are dumping "Total" into a bowl. All of the eleven essential Vitamins and Minerals that aren't used by the plant stay in the bowl. Over time the concentration of some or all of the Vitamins and Minerals increases and increases. It can get quite toxic. An animal pees the extra out. Plants can't really pee. When we pee, we flush the unnecessary extra Vitamins and Minerals away. *Imagine the sound of a toilet flush*
In a container plant environment there are a bazillion bacteria and fungi living. They are breaking down organic material. Just like humans they poop and pee. Large microbiological populations commonly die off because the end up drowning in their own piss and shit.
Striving to give a container plant exactly what it needs, no more and no less, is a lofty and unrealistic goal. Some things are going to build up. Many of them are "salts." These "salts" tend to end up in the lower root zone. Salts are water soluble. They are washed to the lower root zone of our bowl containers. If you water and feed and never let any water drain from the bottom of the pot it only compounds the problem. No poop, pee, or salts get washed out at all.
Flushing is not something to do only when there is an obvious problem. It is something that should be done periodically as a prophylactic (preventative) measure. A fixed screen SCRoG makes flushing a difficult proposition, to say the least.
I have much more to say about flushing and flushing technique than I've said but I'll restrain myself unless anyone wants to talk about it more..