How did I kill my dwarf neon rainbow fish?

Hi

I think I know the answer already but given that I've only been doing this aquarium thing for six months, I thought I'd check with y'all in the Beginner Discussions thread still.

Here is my 2ft tank - excuse the rather odd image which is a reflection of my gas heater in my study.

In a panic I just checked pH, NO2, NO3 and NH3,NH4 levels. My NO3 looks slightly high but everything else looks fine.

But this morning I found one of my female rainbowfish (I had three females and three males) dead in the moss. The moss was a relatively recent addition because I bought some shrimp and figured they could do with some shelter - but maybe I put too much moss in the tank?

Was this just an unfortunate thing? Should I be fluffing the moss up more? Do I have too much moss? I did notice at one stage that some of the fish poop coming out of one of them was thick and brown, but then sometimes went white and stringy but then back to thick and brown. Could it have been a stomach issue perhaps?





Any thoughts? Any direction you can give me? Given my rainbowfish's size I never thought they'd have any problems with the moss. They also all look visibly healthy from what I can make out.

 

Hello,

I doubt it was the moss or the nitrates. 5 ppm isn't much. When you say everything else looks fine I assume they are all zero except for the pH which needs to be a consistent value. Sometimes fish just die while others in the tank are fine. How often are you doing water changes, how often and what do you feed them, has anything changed in the tank recently? At this point it really can be anything.

 

From here the best thing you can do is keep an eye on any changes in behaviour, including eating, and physical appearance among the remaining fish. If anything does change, let us know here and maybe it can be an indicator of what went wrong.

Keep up with your regular maintenance schedule otherwise. Hopefully it was just a touch of bad luck.

 

Hi, thanks for taking the time to reply.

I change 1/3 of the water once a week. I switch between two types of Hikari food - micro pellets and I can’t remember the other.. for them. You’re right, everything is zero except for PH which is around 7-7.5.

Two other thoughts occurred to me.. I use a HoB but it feeds straight back into water with out much agitation so I am going to add an air pump. Occasionally I’ve found one of them farting and splashing at the surface but thought it rather me giving one of them a fright or something as it was never a group behavior.

I keep the water temp between 24 and 26 given that weather has been cold of late. This morning when I found it dead the temp was 24 but that’s not to say it may have been colder through the night as the temp in my study was 14!

Secondly I thought that maybe the issue related to not having changed the charcoal filter things in the tank for a while. That and maybe it could do with a gravel clean. I’ll buy more charcoal filter later today.

 

Do you treat this water? or is it straight from the tap? Do you add it cold or allow to reach room temp? What is the pH of the water? Although all of these would have resulted in mass death.

Probably not an issue. Fish would all be at the surface gasping for air if there wasn't enough in the water.

If it was this all of them would have died.

Good idea to change this frequently but again this is unlikely as only one fish died. This really just polishes the water.

How often do you clean the gravel? Possibly only the one fish was exposed to something as you were cleaning. If a toxic compound was released into the water all of them would be dead.

It may just have been an issue with the one fish. I see this when I breed all the time. Some die, others grow well and are healthy.

 

Thanks TheGrissom. My gravel / substrate is fairly new and besides washing it thoroughly before putting it in the tank a few months ago I haven’t really thoroughly vacuumed it since.

I just recently discovered a cleaning trick with a plastic bottle and an air stone I want to try soon.

When I change the water I use Seachem Prime to treat it and use water that is a similar temperature from touch, if not slightly on the warmer side.

 

Very strange, do you know the age of these fish?

 

I am going to guess that they're between 6 and 12 months old. I purchased all six in one go from a local pet shop while they were pretty small and all of a similar size. You could only differentiate male from female by fin colour. Given how long they take to grow, they must've been somewhere around 3-6 months old when I got them and that was about six months ago.

Only other thing I can think of is that I do have a small molly in the tank as well as an otocinclus. It is rare but I've seen the oto pester the rainbowfish before (I've started adding some algea tabs to alleviate the oto's hunger pangs) and I've seen the molly pester the rainbowfish as well. Once it seemed like the molly was trying to eat the poop coming out of one of the females. Rude. I don't know whether the molly might've just pestered the female into distress but think it unlikely.

Oh well. Will do some gravel cleaning just to get rid of some detritus and keep an eye on the remaining fish.

This gives you an idea of what they look like:

 

So no more fish have died, touch wood.

In fact that is the only other thing that may have contributed as a week or two earlier I had put that small piece of driftwood in and it has been changing the colour of my water ever so slightly. (I did soak and boil the wood for at least six to eight hours on-and-off, prior to putting it in the tank.)

Thanks for everyone's help!

 

That gravel you are using. I have the same in one of my tanks. When I washed it before using it I found 2 coper staples in it. Probably a once off unlucky experience but worth a check next time you clean.

 

Ah, good suggestion. I will probably avoid buying normal stones/gravel in clear plastic again and will only by branded substrate in the future. Thanks again.

 

Yes mine was also not branded, it looks like those staples they use to on thick plastic bags, rather big so easy to spot.