This is why ppl like @ttystikk and others use chillers. They are designed for constant usage and are highly more efficient than a refrigerator or freezer. You'll save a lot of time and money just buying a chiller than dicking around with all these DYI solutions. I learned my lesson. In addition...
Sump pumps are meant to go on and off. I don't know about continuous usage. I used a heavy duty pond pump to service my 16 station, 2 tier veg room without a problem. It had plenty of flow push 4' up, I am sure it could have handled 6'. I believe it was a 1200gph. Got it from pet mountain...
I used that exact air pump in a 16 bucket RDWC system, but I also used a chiller. I insulated my 5 gal buckets and the whole system. Each bucket had 2 large airstones! Massive bubbles and cool water (constant 68). Never saw root rot, don't even know what it looks like. Saw massive white roots...
Yes, it uses less energy. If you hookup a kill-a-watt meter to the input of your system, you will see as you dim there will be fewer watts at the wall; less current same voltage, fewer watts. You are saving energy.
Definitely pick up an ECC/PH/?? Meter. They are worth the money in the long run and take the guess work out of daily maintenance. You can find them everywhere.
Depending on your setup and how your drip is plumbed, you have extra pressure in your main line. Can you show a picture of your setup? If your main line is above your drippers, then it's probably just draining the remainder of the line.
Very nice. I like the detail to neatness by tie wrapping everything. Very clean. Same with your control panel. One question, why didn't you wire the power supplies directly in the power boxes, vs. going to plugs and outlets?