Fish lying on bottom of tank

[BeyondTheLimitsOfAcceptability]

Have two fancy goldfish, have had them about 15m. Normally do 25% water changes as little as possible, but they've recently had a 50% water change as their tank was bogging. The tank glass had a good clean, stones and ornaments left uncleaned though. This was about two weeks ago, they've had water topped up since then but not taken out as it had evaporated. Today I've noticed theyre lying on the bottom of the tank. Just got up to take a picture and they swam away though!

I'm guessing there is a problem with the quality of the water and i need to change it, but am worried about whether it was the change before that has made them poorly now :(

Especially paranoid as we had two snakes who both died a couple of years back, having had them for years and not changed anything. Two toddlers, so I'm also worried that one of them may have done something to the tank.

Thanks :)

How big is the tank? Large water changes are not bad for fish, as long as the water you are putting in is the same temperature and pH. What do you mean you changed as little as possible- do you mean amount or frequency? When did you last clean the filter and when did you do it? Have you got a water test kit?

Are they sitting or lying on the bottom of the tank? Lying on the bottom usually means curtains for the poor fish, but they can come back with a bit of TLC. Sitting on the bottom of the tank is a sign that something isn't right but it's not as bad as lying. Are they holding their fins close to their bodies? Sadly, fancies are prone to all sorts of health problems because of overbreeding so it's really important to keep the water in top condition and give them the space they need.

Have you tried picking up a water test kit? You can get one from most big pets stores and they will let you identify whether there's anything wrong with the water or not.