[quote=“lupillus”]did you fill it with a lot of tap water?
If you suddenly put a lot of tap water into the fish tank straight from the tap, the chlorine used to kill bacteria will kill you fish too.
Fill a basin with the amount of water you plan to put in your tank 2-3 days before you change the water so the chlorine goes away.[/quote]
Interesting. In the states I had several tanks up to 60 gal w various types of fish including cichlids, which can be a little difficult (mostly because they’re territorial, unlike guppies or goldfish, and often kill each other), so I got the hang of aquariums and did fairly well at keeping them happy and healthy.
Then in Taiwan, my last apartment came with a huge fish tank with several giant bubble-eyed goldfish and they did well under my care. I made sure the filter was running properly, cleaned the glass and changed about 1/3 of the water from time to time. But I never let the water sit as you suggested and it didn’t matter. My past experience has been that fish love a water change, because it removes much of the shitty, toxic water and replaces it with fresh water full of O2. After the turbulence settles down, a few hours after the water change, the water is much clearer and the fish are noticeably more colorful and apparently happy, flitting about energetically. Perhaps with a very large tank, there’s enough of a base of stable, old water that the impact from the new tap water is not so harmful.
But a few months ago I purchased a very small tank and it’s been nothing but trouble. I let the initial water stand for a few days and then started slow, buying only 5 fish, when it seemed the tank could hold a few more. But 3 died, so I scooped them out and bought replacements. Again, a few died, I scooped them out and bought replacements. Finally, I’ve been down to just one fish (a neon tetra) for the past month or so, and I feel very badly for the poor guy. I suspect it is lonely and probably struggling to survive in a toxic environment. To be honest, I’d like to put the fish out of its misery, flush him down the crapper and discard the tiny tank, but I couldn’t kill him when he’s been so strong.
So, I don’t know exactly what the problem is. I suspect it’s largely that the tank is too small. Even though the fish has plenty of room all to itself, I wonder if there’s a certain size of tank that is simply too small to develop the equilibrium of oxygen and organisms in the gravel that eat the shit, etc. And when I do water changes in this tiny tank, perhaps the tap water chemicals are simply too intense. Although I never needed to do so before, I will set water aside in advance for my next water change and see if he seems to be happier. I would imagine the tap water is more toxic in Taiwan than California, but don’t know for sure.