Can I cycle my tank if I have fish in it?

Question

I found a dead pleko with furry mold growing on him and I'm afraid he's been dead so long the tank could be poisoned. Do I change all the water and start over? What do I do with my fish till it cycles if I can't do it with them in there?

Answer 1

I agree with Surfside here. What you saw on the pleco was one of two organisms - Saprolegnia or Achyla. These were once considered fungi, but are no longer classified as such. The spores of these are present in most water sources, so it's not something you can eliminate easily - even if you do, it will come back with water changes.

These were probably not the cause of the pleco's death, but more likely a seconday infection - one that attacks an already weakened fish, or one already dead. What you need to find was the cause of death. If your tank is new and not fully cycled, the ammonia might be the cause (the death of a fish will also increase ammonia in the tank, so if you just know that your ammonia is high now, you can't say if it was the cause or an effect of the death). At any rate, a water change is in order if you have other fish in the tank. Do around 25% today and another 25% tomorrow. If you ave a test kit, continue partial water changes until the ammonia is gone.

Another possible cause of death with plecos is starvation. If there's not enough algae in the tank, their food should include algae wafers. Other herbivores and omnivores will eat these as well. Since plecos are primarily nocturnal, if you feed too early in the day, the pleco might not have been getting enough to eat.

Have you checked your pH? As long as it's within a 6-8 range and doesn't fluctuate, this should not have been a problem.

I'd say with other fish in your tank, do the partial water changes as recommended above and use a test kit to monitor your ammonia and nitrites to judge when to perform water changes (so as not to lose any beneficial bacteria you've already established) and be careful not to overfeed, which will also contribute to water quality problems. This may mean twice weekly water changes for a while, but the only alternatives would be removing some/all of your fish and starting the cycling over from scratch, which isn't advisable (or useful) for removing Saprolegnia or Achyla.

Answer 2

There is no need to remove your fish from the tank. It only takes 1 day for the fuzz to start growing on a dead fish, and it is very unlikely that it is going to really affect your other fish.

Clean the tank thoroughly, and do a 30 to 40% water change, and keep an eye on your other fish for any signs of illness. There is no need to start completely over, in the long run that would probably stress your remaining fish more than a recently deceased tank mate.

Good Luck.
E.

Answer 3

Do a 50% water change - wait 3-4 days, do a 50% water change. Let cycle.