The first thing to note is that this picture is not wear my goldfish normally live. It is our hospital tank. Unfortunately, we have not invested in a larger hospital tank at this time because we didn’t think we would need to. I guess we will re-consider that at some point soon. The hospital tank is 10 gallons with no decorations and a sponge filter. Currently it is a high salinity with a low-mid pH of 6.5/6.7. We seem to have rather low pH water from our taps. I’ll get back to that.

Normally, I have three commons and five fancy baby goldfish that live in a 55 gallon glass aquarium that uses two sponge filters rated 100 gallons each and a Fluval 307 canister filter. At the time I was not aware of how quickly the common goldfish would grow so maybe the 55 gallon cannot accommodate them anymore. But to lose four of the baby fancy goldfish in less than 24 hours? We are confused, and also admittedly, really kind of heartbroken.

Here’s what I know so far: One, the goldfish tank was on a near to perfect cycle for the last 6 to 8 months. We have course did regular water changes about 20% every 2 to 2.5 weeks. There is usually minimal decorations, so they were our only visual indicator that algae was beginning to grow. By Wednesday, it was almost completely out of control. Despite turning the light off for the last two days, algae was on all the sides, even pooling near the filters. We figured that the test results would be off because of the amount floating in the water so we did a larger than normal water change about 25-30%, cleaned the sponge filters, remove decoration, cleaned airlines, scrapes the sides, vacuumed the sand and used a preventative algae solution that was recommended to us by big box pet store. We did the recommended dose on the bottle. Within 24 hours our water was cloudy still and the fish looked to be lethargic. We tested the pH and it was very low at around 6.0. We used the recommended dose of “pH Up” from the brand API. The water never got clearer and the fish didn’t seem to be active. We waited 24 hours and did another water change and did not use the algae solution because it did not appear to grow back. However, this time we used “goldfish protect” from the brand API - and while I don’t know what happened all I can say is with that within a day we had lost four of the baby fancy goldfish.

I understand that there are so many more experienced fish keepers here and I’m really hoping someone can give me some input and advice. We truly are very sad to have lost our pets and we don’t know what happened or what we could have done that would’ve given us this outcome. Maybe we interrupted the cycle to such an extent that it couldn’t recover? I don’t know. But in the last couple years of keeping fish, I have only ever had issues with goldfish. Our tropical tank, which houses so many different types of fish has been perfectly cycled for over a year with minimal intervention from us and there’s even more fish inside in a smaller tank. I just don’t know. We also keep turtles and use Fluval filters without issue.