Understand what you're saying. I'll cut the light intensity because as you said 2 tubes might be too much (although it's been ok for over a year before the problem started, and in the past month or so it's only really on for no more than 3-4 hrs a day) so worth giving it a try.I really don't understand the need for such drastic action. The fish are not that badly off now, so why stress them by catching/moving them unnecessarily? This is the highest form of stress fish experience, being netted, because it is the same thing as escaping a predator for your life.
Reducing light some, and keeping up with a good regime of water changes and not overfeeding will deal with this, just give it time. And it is not really hurting the fish as I say.
My concern is that the plants and fish are slowly dying off, and I'm really only just keeping it clean by a 2 hr cleaning session every week with a complete tank and filter strip down & water change. I'm not sure how long the remainling fish can survive for if I don't do anything soon.
Also I've only got a small number of fish left now, and I hardly need to feed them much and things are not getting any better in the past months, hence I'm getting desperate.
I agree, trying to catch the fish is really going to stress them out, and that's if I can even get near them when they're hiding in amongst the plants and decors. The treatment says it's safe for fish and plants, may be it's better for the fish to be left in the tank during treatment?
If this doesn't work then I might have to strip the tank completely, fish out, and blitz the whole tank and start from scratch. Either that or I watch it slowly turn into a green goo of a fish grave yard and the plants turn into a wet pile of composs . . . . (