librarygirl
Look It Up
Hi and welcome! As others have said you added too many fish too quickly; the ammonia levels rose and likely killed the fish. Also it's not the greatest idea to trust the pet stores when it comes to stocking; rainbow sharks need a larger tank than 30 gals. Also not sure what kind of catfish you had but if it's a pleco, some of them can grow over a foot long.
Cycling a tank means growing the beneficial bacteria you need in the tank (mostly the filters) to keep the toxin levels from harming the fish. When fish excrete waste, they produce ammonia. In a new tank without enough bacteria, the fish end up swimming in rising toxin levels unless water changes are done to keep the ammonia (and eventually nitrite) at safe levels.
You have two options right now: either do a fishless cycle with pure ammonia or you can try another fish-in cycle with a few small fish but you'll have to be dedicated to daily testing and potentially daily water changes for 4-8 weeks.
Here's a guide that explains cycling: Guide to Starting a Freshwater Aquarium - Aquarium Advice Read the links in the guide on fish-in and fishless cycling and decide how you'd like to proceed. We can help along the way during whichver method you choose.
Cycling a tank means growing the beneficial bacteria you need in the tank (mostly the filters) to keep the toxin levels from harming the fish. When fish excrete waste, they produce ammonia. In a new tank without enough bacteria, the fish end up swimming in rising toxin levels unless water changes are done to keep the ammonia (and eventually nitrite) at safe levels.
You have two options right now: either do a fishless cycle with pure ammonia or you can try another fish-in cycle with a few small fish but you'll have to be dedicated to daily testing and potentially daily water changes for 4-8 weeks.
Here's a guide that explains cycling: Guide to Starting a Freshwater Aquarium - Aquarium Advice Read the links in the guide on fish-in and fishless cycling and decide how you'd like to proceed. We can help along the way during whichver method you choose.
