Fish Keep Dying And I Don't Know Why!

[eeemileee]

Hi
 
I have a 10 gallon tank that has been set up since January. It currently has:
2 x Dwarf Gouramis
2 x Dalmatian Mollys
2 little catfish bottom feeder fish, not sure exactly which one,
and 1 Platy.
 
Last week 3 Platys died, and I have no idea why. I would like to get some more fish, but want to find out what is going wrong before I do.
Just tested the water and the Ammonia levels are 0.25ppm, the Nitrite 0ppm, the Nitrate about 40ppm and the pH around 7/7.2 
 
As far as I can tell from google these are fairly ok? Nitrate maybe a bit high, but would that kill them?
 
Does anybody have any insight as to what I am doing or have done wrong?
 
Thanks.

 

[ReddSamurai]

Ammonia should be 0 as thats more harmful/toxic to the fish. have you put anything in the tank? was there anything on the dead fish?

 

[eeemileee]

I use tap safe stuff when I put new water in, but not put anything other than that in. Nope, nothing I could see.

 

[techen]

Sounds like you are overstocked in the tank.
 
Nitrate is fine, Ammonia could be zero depending on what test kit you are using.
 
What is the tank temp at?
 
When do you do water changes?

 

[TwoTankAmin]

While your current ammonia reading, in light of your pH, is not a big concern as long as it doesn't last more than a couple of days, the problem is this may be a reading that has come down from a higher one.
 
There should be some amount of nitrite showing up as a result of ammonia. The nitrite should show up after the ammonia. If it does not, that may mean the ammonia reading is not real.
 
Nitrate at 40 ppm (and again if this is an accurate reading since nitrate kits are notoriously unreliable) should not be killing your fish. It is a bit higher than one would ideally like but certainly nowhere near fatally so.
 
When you say the tank has been up since January, does that mean all the fish listed above have been in it pretty much the entire time or were some added more recently? And if no fish were added. has anything else been added to your tank such as new live plants or a piece of driftwood?

 

[CoryLover95]

That tank is very overstocked.  Also, could you post a pic of the catfish?  It's a big problem not knowing what kind they are - you don't know how big they'll get!
But I'm not trying to bash you.  It's a very common mistake.  And now to address the problem of the ammonia.
If you are using the API test kit, it's very important that you view it in natural light.  If not, 0ppm will look like .25ppm.  My guess is that it is not "real" ammonia because of your 0 nitrite, but it could be that there just isn't enough bacteria to handle all of that waste being put out by all those fish.
Also, do you have an airstone in the tank?  Because if you noticed the fish gasping/swimming weirdly before it died it could be a bizarre form of oxygen deprivation.

 

[eeemileee]

I've been doing bigger water changes more often for a while, and the Ammonia seems to have gone, but the Nitrate staying at about 20. If I am reading the chart thing right anyway.
No more have died since though  
 
Hmm well I got the fish in staggered stages, so not all been in since January, but none added recently. 
Yes I have an air pump thing.
Will try and get a picture of the catfish, but although you say the tank is overstocked, they all manage to hide most of the time!
When I got them was told they shouldn't get too big, and that they get red on their fins occasionally. They are about 2cm long each at the moment.