If you have a bucket you can put a heater in so it won't cool off in a couple of hrs, put the fish in there and turn off the heater in the
tank. Then change all the water in the tank or at least 80% of it. Put back some fresh water and turn the heater back on. When the water is back where the fish are used to that temp you can put them back. You have mostly rooted/slow growing/low light plants.
They aren't going to use up nutrients near as fast from the water. You need to only use one light as it's not really overkill to have it
like you do with the second on partial time but not with nothing using up the nutrients in there.
I would buy me a large handfull of floating Hortworth and just tie it with a piece of string around the filter intake. Let it grow as it
pleases but just trim it to keep it from taking over. This will(eventually) hide the intake but will take up those nutrients for you.
Once it gets growing well you can put the other light back on it's partial cycle. A simple solution if you don't want to wait till some
stemmed plants get a good growth on them. You'd need to put at least a few, like two bunches of Rotalla for example(spread out
and having each stem planted separately) to equal that floating Hortworth for absorbing nutrients. Litterally tie the Hortworth
around the intake(not tightly) and it will mostly grow upwards till it goes along the top if you let it. Trimming a bit each week
will keep it good looking. Only a suggestion...
ANY direct sunlight will make it very hard to be rid of this type algae until something is done to use up some of the nutrients.
My daphnia culture tank 2.5g with 2-3 hrs of direct sunlight per day.