Melanotaenia praecox (Neon Rainbow) dying

[remoore]

Help...

I had 6 Melanotaenia praecox in a 20 gal (set up a month ago) with 5 small Calvus, 3 small Haplocromis Insignis, 3 small Aulonocara flavescens and a Golden Nugget Pleco. Everybody seemed to be getting along nicely. I have been doing water tests every 3-4 days since I set it up and have been doing 20% water changes every 2 weeks. I am running a Aquaclear 500 (I know its overkill). I have never had any positive tests for Ammonia or Nitrite. My ph is at 7.6 and water temp at 81-82 degrees. Everyone seemed to be eating well and mobile. Suddenly yesterday I lost two of my Neon Rainbows and today I lost another one. Any ideas as to what is happening?

 

[lmw80]

Hi remoore, and welcome to aquarium advice!!

First things first. Your tank is overstocked. While the species may have no trouble getting along, there is too much in there for a 20 gallon tank.

Also, to help us better asess (did I spell that right?) the cause, please let us know what signs there were before or after death, ie, behavior, bumps, rot, etc.

Did you add any fish recently before these deaths? Do any of your remianing fish exhibit any odd behavior or have any physical signs of illness? Any other details would be a great help.

 

[remoore]

I got the Rainbows a month ago. I had them a week and added three of the cichlids. A week later I added the rest. They have all been together for two or three weeks. I know its a lot of fish but they are all very young (only the haps are over an inch in size) and they are all being moved to my 180 gallon in the spring when I put my koi outside. I also am over filtering with the Aquaclear 500 so I don't think the number of fish is the problem.
There was no indication to me that anything was wrong prior to the deaths. Everybody was getting along and all were and still are eatng and swimming around just fine.
I understand that Rainbows are a quite hardy fish, especially compared to the Calvus so I expected the Calvus to go first if there was a general tank problem. So far the only problem is with the Rainbows.

 

[lmw80]

Ok, it's good you are moving the fish to a bigger tank. That issue is out of the way.

My next thought comes from the cichlids. Although I have never dealt with cichlids other than angles before, I have heard that they are very territorial and can be quite aggressive. I know you said everyone was getting along fine - did you observe when the light was off? I obtained 3 angels when I obtained my 46 gallon tank. I thought everyone was getting along fine, but two of the angels seemed to slowly be getting worse. I finally figured out that they were fighting....I mean ramming each other at night, when the lights were out.