Ok
There's a plant called hornwort...it requires almost no care, is one of only a few that I know that grows faster than they Munch it, and it loves cold water. If you get some of that in there, it will make use of the ammonia, excess nitrates, etc caused by goldfish being generally dirty fish
When you clean your tank, clean from the bottom first.....use a syphon to vacuum up all the mess they leave in the substrate. If you have gravel, you can push it in for a second and watch the dirt suck out through the hose
They don't need feeding as often as the package says....a feeding once a day is fine. You can even give them vegetables
mine love broccoli, spinache and they
love melon! You can leave veggies in for a few hours and fruit for an hour. It's a great supplement to the diet, and fulfills their need to graze, so they don't get bored and redecorate lol
If you see air-gulping, rapid gill movement, or just sitting in the water not moving....do a water change. They produce insane amounts of ammonia and it can sneak up on us
Over-filtration is your friend
. If you have a 7gallon tank, I suggest a 20-30 gallon filter. Aqueon quiet flow 30 is an amazing budget filter for goldfish and cleared up ammonia in my tank within an hour of adding it. It's easy to maintain and has never clogged.....though I suggest a prefilter sponge on the intake tube....my goldfish killed my aquaclear by spitting sand at it [emoji13]
The best water conditioner is Prime....in fact I suggest Seachem sir all additives, though I will use API if I can't get Seachem. Prime
I'm sorry if I overwhelm you with advice...if you have any more questions please ask- I'm no stranger to overstocked goldfish . I owned two comets for years in a 29 gallon before adding them into my dads pond. Right now I am wintering all four 5-6inch goldfish in a 38 gallon