First of all...read that entire post about Breeding Beneficial Bacteria from Heisenberg, it is gold.
Next...I have a seen that image of foam/froth on top of my reservoirs on a daily basis. I breed the bennies and add them as prescribed in Heisenberg's post (link below). Doing this causes foam on top of my res because that is the bacteria thriving and multiplying.
All that said, I have also had other things produce a foam on top of my reservoirs (DWC, ebb & flow, aeroponics).
So to answer some of your questions...29% H202 should be mixed in a 1:10 ratio with water. (think...a 30% solution diluted down to one tenth of its strength is 3%, so you can produce the 3% h202 that's more common by diluting the 29% that way)
This has been said, but I'll agree...Great White = beneficial bacteria and fungi. It will die when used in conjunction with H202 or any other fungicide.
So the foam...what to do...the answer is multi-part. But the foam in and of itself, isn't going to hurt your plants...its more often a sign that something (bacteria, fungi, etc) is thriving in your reservoir. (whether it be good or bad is to be determined)
If your prepared to flip your reservoir, then this is the best approach and is a combination of what all others in this thread are saying so far....
1. If you're worried that bad bacteria are in your system, which could cause that foam, then I would add extra oxygen to your reservoir. Because bad bacteria are, for the most part, anaerobic. Whereas bennies are aerobic and thrive in highly oxygenated water.
1.1 If you're worried still about bad bacteria causing that foam, then consider trying to starve the bacteria (both good and bad). Bacteria of both types need food to reproduce, starving them will do the obvious and they will die. Bacteria, again both good and bad, thrive on broken down organic material. Bacteria itself will break down organic material, but a 'Zyme will speed this process up. So, if you're adding a 'zyme product like Hygrozyme, then you're actually producing food quicker fir bacteria will thrive off of. This is a good thing if you have only beneficial bacteria in your reservoir, but if you're worried about the bad ones then you should halt the adding the 'Zymes. Instead, you could allow both the bennies and the baddies die off through starvation and then replenish the bennies by adding more every 3-4 days.
In addition, temporarily stop adding any organic supplements like Super Thrive. Bad bacteria could benefit off of that too. Only add stuff that could possibly feed bacteria when you're sure you don't have bad bacteria that you're feeding. (it makes sense but I didn't think of it either at first)
2. You must try to start with a sterile environment. I use 1.5% H202 and Physan 20 for a 24 hour period to clean any equipment, doing this creates foam on top of the water that looks similar to your pic. I don't submit the plants to this process. I actually try to have back up equipment ready to be sterilized and used in situations like this...that way the plants don't have to sit in a temporary holding area while I sterilize their reservoirs.
3. Once you're happy with sterilization and everything has been rinsed thoroughly, you should immediately inoculate your reservoir with beneficial bacteria, as mentioned in
https://www.rollitup.org/dwc-bubbleponics/361430-how-breed-your-own-beneficial.html.
When I get a reservoir that needs flipped due to bad stuff in the water, this is what I do:
1. sterilize everything (tools, equipment, reservoirs, etc) and rinse the plant roots off with tap water
2. rinse everything super well
3. inoculate the new reservoir with the EWC tea (bennies from the link above) and I even do a little redundancy...and add sub culture B and aquashield.
4. add the plants back in and wait 72 hours (in the 3 days of waiting, I always see foam on my water because of the bennies...but it eventually subsides...and then I add more bennies! I want that foam because I know its a sign of good things happening so long as the plants don't have any adverse affects that I can positively correlate with the tea.)
In sum...I've seen this foam. For the longest time, I was in the same boat of like...WTF is going on here and then I would flip my res over and over again...mostly just dumping bennies down the toilet. I didn't realize at the time that the foam was a sign of a good thing. Since then, I've learned to wait it out and let the plants tell me whether or not they like it.
If your water smells bad, not earthy like compost tea, but sour or rotting....then that's a sign of the anerobic bacteria and the res should be dumped. If your water smells like dirt or compost (aqua shield is liquid compost tea, it says it right on the bottle), then I would let the foam be because that earthy smell is a good sign....as long as you can breathe the smell and not bunch your nose, then that's the scientific test I use to judge whether or not I have bad or good bacteria in my waters. If you're unsure what bad bacteria smells like...well...take some of your res's water and put it in a jug...put that jug in your closet for a month and then go smell it. LOL, it'll smell horrible because of the anerobic (oxygenless thriving) bacteria are just loving life...smells like rotten eggs.
Last but not least...ask more questions and don't be afraid to. No question should be taken as annoying or too detailed...so ask away.
