10 Dead Fish [Updated]

[TheFishEnthusiast2015]

Hi,

I have had an established fish tank since August 2014 although recently have had a snail problem. I was advised by a local pet store to do a full tank clean out (replace gravel with sand and filter changes) along with 50% water change.

I arrived back from work today with 10 dead fish.

I have a 125l tank and fluval u4 filters. It just has small fish in so mollies/neons/platys. My blue ram has changed colour and looks like it's about too die too.

Any ideas?

 

[snork6]

How long have you had the mollys/platys? Where I get mine they are not that healthy and can die from big changes.
 
 
Also I wouldn't suggest taking advice from large chain pet stores.

 

[DrRob]

I have had an established fish tank since August 2014 although recently have had a snail problem. I was advised by a local pet store to do a full tank clean out (replace gravel with sand and filter changes) along with 50% water change.

Any ideas?

 
What do you mean by filter changes? Did you switch out all of the cartridges in the filter for new ones? Or wash them under chlorinated tap water?
 
Whilst waiting for answers, best advice I can give is lots of clean water. I suspect that you're dealing with something toxic, either from new products in the tank or from losing too many filter bacteria in the clean out and going into a cycle. Either way a 90% water change will dilute whatever you have to 10% of it's strength. If you have test kits, then now is the time to be using them and checking your numbers as well. So drain the tank down to the lowest level you can, and refill with temperature matched, dechlorinated water.

 

[Byron]

I agree, and from the info I would suspect poisoning from ammonia and/or nitrite.  Replacing the substrate removed the majority of nitrifying bacteria, and replacing the filter media at the same time got most of the rest of them.
 
Do the tests Rob suggests, for ammonia and nitrite, and if either is above zero, do a major water change.  Using a conditioner that detoxifies ammonia and nitrite during this is advisable.  Prime and Ultimate both handle these, there may be others.
 
Byron.

 

[Crystal90]

Not sure what kind of snail problem you had but if it's just too many snails growing there's an easy way to control them. I found that they will lay a small jelly-like sac just above the water line. If you just wipe off the sac with a paper towel, you can easily stop them from reproducing. I did this and controlled them quickly. This way you don't endanger your fish with drastic measures.
 
Just my 2¢.

 

[the_lock_man]

From the minimal info given by the OP, I agree with Rob and Byron. Nothing further to add, apart from asking you to post the water test results on here so we can confirm the diagnosis.