I have had a number of goldfish (three pairs of two) over the last six months or so. In all cases they have lasted about 2 months before dying. I have no idea what I'm doing wrong so here is all (hopefully) the necessary info, if anyone has any idea what I'm doing wrong please let me know.
- The tank is 25 litres (I know it'll need upgrading when they get bigger but they never get that far).
- There are three plants in there with a plastic log for the fish to hide in (I used to use a wooden log but I switched to a plastic one just in case the wood was causing a problem). There is gravel at the bottom of the tank.
- The pump is a Marina i25 and the cartridges are replaced every two weeks or so. I used to use the pump that came with the tank but upgraded to make sure it wasn't the cause of the problems.
- I do a partial water change every week/10 days:
- I siphon some water into a bowl.
- I use a net to get the fish out and put them in the bowl.
- I clean the glass with a microfibre cloth, and clean the pump (replacing the cartridge if necessary).
- I siphon out about a third/half of the water into a bucket and discard it.
- I siphon enough water to top the tank back up. This water has been dechlorinated with Tap Safe and left in the bucket for 24 hours to come to the same temperature of the water in the tank.
- I leave the tank to settle for half an hour or so and then put the fish back in, discarding the water from the bowl they were temporarily in.
- They get fed with coldwater fish food every other day. I give then a pinch of food and they will almost always eat it all. A couple of times a week I feed them shelled peas - they seem to love them!
- The fish aren't always from the same shop (or even the same chain). I've had some fancy ones but resorted to the bog standard "hardy" goldfish in an attempt to make them last longer.
- The water has been regularly tested at the local pet shop and they have never found anything abnormal about the levels.
- In the past I have tried to treat them with salt but all this does is kill the plants, the fish don't get any better.
- After one pair of fish die the tank is emptied and cleaned (just with warm water) and refilled before adding more fish.
I know this is a very general question but I would appreciate it if anyone has any advice, it is slightly disheartening that I seem to manage to regularly kill off pets that are supposed to be very easy to look after. I feel like there must be something obvious that I'm doing wrong.