I have a 36 gallon bow from freshwater aquarium with 4 fish in it (2 comet goldfish, 1 black moor goldfish, and 1 common pleco). I have no live plants, no snails. The tank has been established for almost 2 months and everything was fine until I noticed that all of my goldfish have black scales. A quick google search shows it if from stress. Ordered a master test kit and find out that the Ammonia is off the chart, my Ph is 8.0 (and I used the high Ph test kit) and ,my nitrate level is 0. I'm sorry but I don't remember what the nitrites were.

I have vacuumed out all/most of the sludge in the gravel. I have stopped feeding the fish (they weren't eating anyway). I have done a partial water change and put in the Ammonia lowering chemicals.

My plan was to do another water change today and then add the Ph lowering chemicals.

What else can I do? Did I miss something? Any and all help/advice is appreciated! Thanks!

Goldies don't mind higher PH, don't mess with it. Doing so can cause all sorts of issues.

If you are showing no nitrates your tanks has not cycled properly. Hate to say it but your tank is also overstocked. (20gal for the first goldfish and 10 gallon for every one after). Get rid of the common pleco, they grow far far too large for your sized tank.

You have yourself a tank of poop machines, goldfish are pretty much what goes in, very shortly after comes out, a very dirty fish that require a lot of filtration, tank room, tank maintenance, add to that the common pleco, which are also major poop producers.

Too keep what you have, not recommended by the way, you will need to do 2 smaller water changes a week.