My plants seem deficient not sure what to do- please advise
I have a 20gal long with 12 fishes (cherry barbs, platies, kuhli loaches, one betta) and some snails. I'm struggling with getting the plants healthy. It's low-light, no CO2. I switched the light source to a "full daylight spectrum" bulb a few months ago, some plants started doing better. I started putting root tabs in (just gravel substrate) and others started improving. I've been dosing with Seachem comprehensive once a week, realize now I should be dosing that every day?
I have java fern, rotalia, water sprite, aponogeton, vallisneria and crypt wendtii. The crypts are doing the best, the rotalia older leaves are small and dark, new leaves growing bright green, much bigger on the top since I added root tab. Apono the leaves get a certain size and then start to turn brown and die away- but it keeps growing new shoots still. Nothing will stay full-size on that plant though. The water sprite it grows leaves continually but the stems rot away. I have pulled it up so the crown is out of water (pegged it with a plastic twist-tie) maybe that will help? Java fern the leaves get little holes in them, get black spots, then turn yellow to white and die. That plant is always growing new leaves too- they look fantastic for a while but when get bigger start to get the splotches.
I read on a chart somewhere that these symptoms (the yellowing and pinholes) can be potassium deficiency so I bought some dry K2SO4 from GreenLeafAquariums but now not sure what to do with it. I read one one of these posts a chart that the dry dose for my tank size should be 1/16 tsp- do I just sprinkle that into the tank, 3x a week? Should I up the dose of Seachem to once a day, see if that helps before I start putting in the dry fert? Or try Leaf Zone and see if that helps... (it sounds easier)?
I was trying to keep this simple (low tech) but now it's getting more complicated and I'm a bit confused. However, I don't want to loose my poor plants! Please can someone help me understand if I'm getting things in the right direction or should do it differently. Thanks.