Okay, I've had a planted tank (125 gal) for a little while that a very knowledgeable person set up. We started it with a few guppies and darters and snails and some grasses and other plants. Everything went great for months. Then a couple of months ago, I got a brown algae slime (similiar to what we get on our rocks on our koi pond). I manually got rid of it by siphoning it out with a gravel cleaner. Ever since then I can't get rid of algae. I scrape it off and clean it and now I have the type that is like a carpet.
I also added 3 angelfish, 2 blue paradise gourami's, some algae eaters(ottocinchlis sp?), and 3 red tetras, a sword plant that had huge leaves on it and a banana plant. All of this was last August and from local breeders that put on the aquarium show in Indy.
I do water changes faithfully (25%) every week. I have 0 nitrites, ammonia, and high ph of 8.8. My kH and gH tests don't do it in degrees, it does it in ppm. Will need to retest, but know that both are high (in 300 range).
In the past couple of months (gradually) I have lost a couple of darters, a couple of guppies, am losing a gourami, have lost all of my snails. I now have a mauvish colored film on the inside of the tank on the back. My plants aren't growing and the little leaved ones are losing the leaves. All the rest of my fish are fine.
I've read Rex's guide, but am not that great with Chemistry. I can water test koi ponds with the best of them and know what to do, but I guess I'm not testing the right stuff with the aquarium.
So now the questions,
Any idea what is causing my tank to go downhill? (only 14 fish in 125 gal)
What exactly do I need to test for in the aquarium that is different in the pond?
I know I need CO2 but am not sure how to use them and can't afford the $225 price tag I was quoted from around here. Sure I can't it cheaper but not sure what I need. don't have the time to mess with DIY stuff (I teach, have 3 young kids, a koi pond, and am working on my master's)
Any advice would be helpful because I sure haven't been able to figure out what is going on.