Hey, just read this whole thread, itâs a very interesting read for me because I want to try HPA albeit on a slightly larger scale. Not for growing pot though, Donât judge me 
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I wish I could though but my living situation doesnât allow it right now. I grew pot before with DWC with a good success (after a few bad trials and a lot of swearing out loud) but then I devised some kind of media-less root-hanging-in-mid-air flood & drain system. The best growth I ever had, it was really good. I even left the system running and flew out of the country for 2 weeks lol⌠but I returned and it was still working perfectly (I over sized the water tank, thereâs no magic happening here). Here is a photo of the system, but I later modified it a little but with the same basic idea:
Those are LED lights btw in the photo, but the camera white balance was adjusted to make the photo appear normal instead of well magenta colored.
So with that, Larry, I read some of the problems you had with PH. I had a hell of a time trying to control the PH at first, I read through every thing. I even remember lading on some Nigerian web page explaining how to control the PH with no success! Well until I did an excruciating step by step analysis and thatâs what I found:
1- I surprisingly discovered that some of the systemâs components screwed up the PH. I prepared two small buckets of PHed water (6.0 PH), one was the control and in the other I put some of the system components. First up was the freaking airstone. I just put the air stone in the water and stirred it up a little (I stirred the control bucket as well) and the PH went up the roof. Turned out that particular air stone was made of god knows what but I suspect it had some calcium bicarbonate (an actual stone! they really stayed true to their word lol). I ordered another one, did the same test, PH didnât change at all.
Second up was the air hoses, I tested them, they actually decreased the PH a little but it wasnât a big deal. Still I ditched them and ordered new one. Again the PH was stable with the new ones.
Third up, I checked all the fittings (i.e. put them in the PHed bucket and stirred then waited for a while). These were okay.
Fourth, the expanded pellets in the basket and the basket itself (separately checked). the basket was okay but the clay pellets messed up the PH a little. I them learned to give them a really really good wash before using them then they stopped messing with the PH.
Lastly, I ran the whole system with only PHed water (no plants and no fertilizers). Just to check if the outside tank or the plant tanks were messing with the PH. The PH stayed very stable even with aeration vigorously going on. At that point I knew my system was okay.
2- Algae/slime messes with the PH and makes the tank smell bad. I was careful regarding light proofing from the get go but I never imagined how important it is. A friend of mine accused me of being anal about it. Thatâs true, itâs one of the most important things. I stuck my mobile phoneâs flash light (itâs powerful) to every thing, the plant tanks and the water hoses and made sure that not even the tiniest bit of light can get through. You see in the photo I put aluminum foil around the plant tanks, I eventually ditched this idea in favor of a light proof tank from the get go, I also checked it by sticking the flash light to the tank wall and making sure no light at all on the other side of the wall. This is my favorite tank for plants: Coleman Party Stacker.
The top of the Coleman Party Stacker needs a reflective sheet on it to be completely light proof, but what I like about this tank is that the inside is white so I can see the water color and the roots very clearly and it looks very clean as well. As you can see here:
The above photo is not DWC btw, itâs actually flood and drain with the reservoir tank outside the tent. The photo was taken when the system was in the process of filling up the the plant tank again. This way the problem of the water heating inside the plant tank (which is inside the tent) was eliminated completely, Freaking root rot never again.
And here with the top covered with reflective film from the time-lapse camera view:
When I did that, the PH stabilized (meaning that it followed the normal behavior) and no slime at all in the tank. The only place I found the tiniest bit of slime was, believe it or not, on the air hose inside the plant tank. That was because the hose was a clear plastic and acted as a fiber-optic so it transferred a tiny bit of light from outside into the tank. But that wasnât a big deal
Well, enough with the PH already. I see you run a sterile tank. I tried that and it worked as long as I put the correct amount of chlorine at a regular pace. The problem I faced with sterile tank was that when I forgot to add the chlorine (after it has evaporated out of the water) the tank suddenly smelled bad. I somewhat figured the problem with running sterile. I kill all bacteria and fungus (good and bad) and I make the system completely sterile, then I forget to add chlorine and suddenly the stage is totally clear for âbadâ fungus or bacteria and they literally occupy the tank. After a few trials (including peroxide, it was my worst ever trial, for anyone reading this DONâT USE PEROXIDE), I ended up running a live tank with bennies. I tried several ones, I tried Recharge from Real Growers (everyone was raving about it) It worked well but itâs not made specifically for hydroponics so it made the water and the roots look bad. My greatest success was with Great White (Iâm not a sponsor btw, yes I know, I wrote all that just to tell you to use Great white lol). Anyway, it worked perfectly and the strange thing and that is true, after I used it, I let my PH swing with no ill effects to the plant. Actually in my latest grow, I never checked the PH even once, I added the nutes, then the tiniest pinch of the bennies (you should only add a tiny pinch, never more) and closed the tank, thatâs it. I also never checked the PPM because I measured exactly what EC to expect from the amount of nutes I add (I used General Hydroponics Maxigrow, Maxibloom and Calmagic) so I know what the PPM to expect. Every thing worked great and it gave a very good yield.
One other mistake I did at the beginning is to follow some bad advice on some of the growing sites and starting with what they recommended at 1/4 or 1/2 the recommended nutes. It not a bad advice perse but I didnât realize at the time that if everything was optimized for perfect growth like the lighting, the temperature and the CO2 concentration (I put the tent in my bedroom to raise the CO2 so I was literally feeding the plant 
" then the bottleneck would be the fertilizer concentration. It drove me crazy for a while because I had nute deficiencies that all went away once I doubled the PPM.
Well enough about this post. But I still will talk with you Larry about your previous HPA trials.
Of course, Google will show you plenty of other options.
