HELP! Fish continue to die for no apparent reason

I set my tank up in December. It's 37 gallons, cycled, and heavily planted. I've been slowly stocking the tank ever since, but fish continue to die no matter what I do. So far I have lost 3 corydoras, 2 platies, 2 guppies, and one balloon molly. Sometimes they hide a lot before they die, but sometimes they drop dead for no apparent reason.

My ammonia and nitrite are always at 0. My nitrate varies depending on the day of the week but it's always below 20. My pH is 8.2. I acclimate all my fish by floating the bag for an hour and gradually adding tank water to the bag until the volume has doubled.

My newest lead is that the tank developed green water last week. But I haven't got a clue if that's connected to the deaths, in fact it probably isn't, considering the fish were dying long before the green water started.

I got the fish from two different stores, and both of them are high quality fish shops, not walmart or petco. The tank is not even close to being overstocked, and there is no sign of bullying in the tank.

I have some theories, each more unlikely than the last:

1) Chemicals in the tap water: Maybe my tap water contains some toxic chemicals that I don't have a test kit for? But that case, wouldn't I know if my tap water had a problem? Also it seems unlikely that every person in my town can't keep fish, because that is what it would mean if the town water was the problem.

2) Water softener: I have a water softener. But, all of Canada and about three-quarters of the US has hard water too, and I assume those people have softeners as well. If water softeners were fish-killers, wouldn't the majority of the country find it impossible to keep fish? Also, my jungle vals are thriving, and they are a plant that supposedly needs hard water, so the lack of minerals must not be too much of a problem.

3) Flourish Excel: Has there been any cases of overdosing this stuff killing fish? I've decided to stop dosing the stuff just in case, but it seems unlikely to be the culprit.

4) Ineffective filter: Maybe the filter isn't big enough or else isn't removing the stuff it is supposed to remove? But in that case, why are ammonia and nitrite at 0? You'd think that would be an indication that the filter is fine.

5) The fish were just unhealthy to begin with: But then, why don't you hear about unexplained fish deaths on this forum? If unhealthy fish were common, then more people would have an issue with them.

6) Insufficient acclimation: Some of the fish died two weeks after I got them, so you'd think they'd die right away if the acclimation was the problem.


PLEASE HELP! I'm getting desperate! I'm pretty close to giving up on fish at this point!

 

You've been on the forum for a while so I'm sure you would understand most of the stuff that is talked about. Honestly I think this is a prime example of getting a QT set up so you don't risk other fish to infections, and diseases.

There are always unexplained fish death, sometimes it's just what it is. Perhaps doing frequent water changes will help out. I would keep what you have in the tank for now and than see what happens in the future.

Don't give up. I had lost plenty of fish in my time as well.

 

I agree!

The QT is vital. You have no idea what the fish have despite being a "reputable" store that you are getting them... Even reputable stores have disease outbreaks, fish that are stressed become more subseptable to diseases and so forth.

At least with a QT, you can observe your new fish for at least 2- 3 weeks before adding them to your main tank. You'll either find that they are okay or not.

 

It sounds like you are doing everything right, except the QT tank and that is something to consider. However, I have lost fish that I purchased a couple of weeks after purchase.

Checking the tank and other occupants in there at the time of those deaths leads me to believe they were due to an unhealthy specimen to begin with-I find that if they make it after a month, unless I do something wrong, they are good to go! Hopefully, the next purchases will do much better!

 

Do you have a salt free water softening system? If it uses salts, look up how they may affect your fish. If not, how soft is your water that you put in the tank? If too soft, the pH can bounce around, leading to stressed out fish and overall unstable water parameters. Been there, done that

I cut hard tap water with vending machine water now for my tetra tank. My cories have acclimated to the hard water, and everyone else is from hard water areas.

I'm assuming you've been communicating with your 2 LFS and examine all of their tanks for any sick and dying fish every time you visit.

 

Don't give up!
I'll second--no third...or maybe fourth? the idea of a QT tank.