Hi, OK, I'm just a noob at this, but know I could fix the problem if it was my tank.
Here's what I would do:
1. STOP all ferts.
2. Use LESS light! Remove the dimmer one. Looks like you have two there. As for light, the watts per gallon rule doesn't usually work so well any more. Base your lighting on PAR, PUR and LUMENS.
3. The filter should pump at least 200 gph min, like a Fluval 50. Clean it but first scrape the algae off the sides of the tank, etc. and let the filter take up all the green stuff.
4. Lower the light to say 8-9hrs a day.
5. Do water changes of 10gal every 4 days or so as to not shock the fish.
6. Use only a pinch of fish food, like Omega One Flakes. Only feed once a day. Some flake foods contain phosphates as preservatives. Check the Tetra label for phosphates!
7. Your pH is LOW, check your tap water for pH and if low or if you are using a water softener, then you might consider bypassing it somehow.
8. Setup and run an airstone ALL the time. Algae die off robs O2 from the water.
9. Whatever you do, don't use a water clarifier cause if the water does clear, you won't know what the real cause was.
10. After you do all the above, you might want to get an API Phosphate PO4 test kit. If you have high phosphates, which I suspect, then you can CUT them down easily by adding a second HOB fliter, like a Fluval 30 or 50 and pack it with API Ammo-Chips AND API Phos-Zorb.
11. You should also consider a power head to increase water flow, but heavy aeration might be enough.
12. You should also check the substrate for iron content. This will help the plants grow, so when things settle down and you have clear water, then you might not have to use so much ferts or CO2. Your plants are small and don't "really" need much now except the nitrates from the good bacteria.
13. When you do see plant growth, go easy on the ferts! (err on the side of less is more)
14. And whatever you do DON'T try to raise the pH with liquid chemicals! Shoot for a pH that's around 7.5. Then, the fish waste will naturally lower it. Then, you raise it back up again with WC's! Simple! The WC's alone should be enough to gradually raise the pH.
Presently, on my 37 gal, use two Fluval 50's. First is set up with Sponge, Bio-Max and Carbon. The second uses a Sponge, Ammo-Chips and Phos-Zorb pouches.
Good Luck! (I like your cats!)
Last edited by Ed's Fish Tank; 02-28-2013 at 12:43 AM..
Reason: Fixed typo and added info