Sick Tank!

I'm no expert but it sounds to me like its probably general poor water quality. Lots of snails indicates overfeeding as snails will only breed if there's surplus food in the tank. This food will in turn decompose and pollute the water. I'd cut right back on feeding, stopping completely for a few days. The fish will be fine. I thing if the whole tank is affected then you may as well treat the whole tank.

What are your ammonia, nitrite and nitrate levels?

I'm not the most experienced fish keeper on here by a long shot, and Sue will probably be best placed to give you advice.

If you were to set up a quarantine tank to clean the main one, you'd have to make sure the tank was cycled before adding the fish as the extra stress could make them deteriorate further. You'd therefore want to transfer one of the filters over as a minimum, provided whatever disease you've got in the tank isn't in the filter.

What are your stocking levels and are all the fish sick?

The problem with moving all the fish into another tank is that the water will quickly become polluted. There are bacteria in all three of the filters and on every surface in the tank - the glass, the decor and even the gravel to a depth of a cm or two. Moving the fish and just one filter will mean not enough bacteria going with the fish so you will have to monitor the ammonia level very closely. Moving all the decor you can cram in the smaller tank would be of some help.
However, keeping a very close eye on the ammonia level in the small tank, and doing a water change if necessary, means that it is do-able. And yes, keep the left over filters in a bucket of water, together with any decor that won't fit in the smaller tank. The bacteria won't starve over 24 hours, but they do need to be kept wet. Use some water from the big tank in the bucket. It would be best if you can turn the filters on in the bucket so the water still flows through the media. If this is not possible, take the media out of the filter and let it float in the water. The bacteria may not starve in the time the filters are in the bucket but they could suffocate with no water going through the media.
And transfer some big tank water into the small tank along with the fish, then if it is a water quality problem the fish won't be shocked by putting them in completely new water. If you put the old tank water back in the big tank after the clean, just topping up with new, it won't affect the fish too badly.


If you could manage to do the clean in one day, and get the tank set back up again within 12 hours, that would be even better 


The clean will kill some bacteria - those on the glass and the gravel. There should be plenty left in the filters and on the decor to make up the loss quickly, but still monitor both ammonia and nitrite for a few days. If you don't feed the fish for 1 or 2 days before the clean (unless you were planning on doing it today  ) that means they would make less ammonia while in the small tank. And feed very lightly for a few days after the clean.





As Cod says, most diseases are down to poor water quality. Poor water quality stresses the fish and stressed fish have lower immunity so they come down with things easier. You mentioned whitespot - do the fish look as though they have been sprinkled with salt? Once the fish are back in the big tank, watch them for signs of disease.
Can I ask what your maintenance regime has been? Eg, how often do you do a water change, how much do you change, do you clean the gravel when you do a water change. Do you use a water conditioner (dechlorinator) when you do a water change.
What kind of tester do you use, liquid reagent or strips?
Do you routinely add anything to the tank other than dechlorinator?
How much do you feed the fish? The usual recommendation is to feed no more than the fish can eat in 2 minutes.

Anything you can think of to tell us will help in tracking down the problem 

Your water change routine sounds fine, though perhaps do one once a week rather than 1 to 2 weeks 

If the substrate is more like coarse sand, does the fish poo etc sit on the surface (like fine sand) or go down between the particles (like larger gravel)? I now have sand in all my tanks but started with gravel, and sand is much easier to clean as the mess sits on top - though it does look a mess when a water change is due.

If you are using strips to test for nitrate, take the reading with a pinch of salt. Nitrate is difficult to make a tester suitable for home use, and even the liquid reagent ones are only ball park. Good practice is to keep the tank nitrate level getting higher than the level in your tap water plus 20. With a nitrate of 25, if that is just before a water change (when it will be at its highest) and you tap water level is 5 or above, that's fine.

I agree that moving fish is stressful for them, so your idea of a big water change sounds best. Using hot tapwater is perfectly OK if you have a combi boiler. It's the older systems like ours where the hot water sits in a tank which is topped up from a header tank in the attic that can cause problems. That header tank is open topped and all sorts of things can get into it. Dead rats have been known  We've had wasps' nests in the attic and I wouldn't risk using hot water just in case there is any insecticide in there from the treatment the chap used.

Did you check all your decor for bad smells? I ask because I once had a plastic wood ornament that was hollow with just one tiny hole in the base - a large pin sized hole. The water trapped inside that stank, so I threw it away.


Good luck with your clean up