Pawl

Tank size: 20 gal.
pH: 7.1-7.2
ammonia: 0 PPM
nitrite: .1 ppm
nitrate: Below 20, I use distilled water with weekly 10% water changes
kH: a week ago they said it was just a little high, but nothing to worry about
GH: I'm not sure what this is.
tank temp: usually around 80 but it can fluctuate about 2 degrees over a day

2 Adolfoi Corydoras
4 Neon Tetras
2 sick White Clouds

My two white cloud minnows are less active than usual and are starting to eat much less or not at all, one is very pale and they are closer to the bottom of the tank than usual. Both of their mouths are blood red for some reason, and one has had an increasingly arched back. It doesn't seem to be very significant but occasionally they will gasp.

I change about 10% of my 20 gallon tank every week, and sometimes a little bit more depending on how dirty my gravel is.

Recently I have used Algae Destroyer, a bit of antibacterial (melafix) from another sick danio about a week ago who had raised scales and the day i noticed i got the melafix but he died two days after i started dosing. I just added some salt to the tank but less than the recommended dose because of the corydoras, who i hear do not like it. I also added some Stresszyme to help my biowheel.

I feed my fish with tetracolor flakes and some pretty cheap fine pellets with ingredients listed as crude protein 50% Crude Fat 15% Crude Fiber 2% and 1.26% phosphorus but usually only my corydoras eat these, every 2 days I'll feed them all frozen brine shrimp.

My filter is a marineland penguin biowheel for a 30 gallon tank that filters about 150 GPH so its a bit over filtered, and their brand of filter media that includes about 2 tablespoons of activated carbon.

I added a new (quite large plant) that grew from a bulb, and I added 5 neon tetras but 1 died mysteriously. I acclimated them using suggested methods. My tank has been running for about 2 months. Recently I had to remove a plant that had what looked like beard algae, and my danio swelled up like a pinecone and i bought some melafix but he still died 2 days later. My substrate is white rocks that are not extremely smooth but have no sharp edges that i bought from Petco. I live in the USA.