4 Dead Fish

[Aquatious]

Hi,

We've had four dead fish in our large tank in the last few days. We haven't had any die in the tank for about a year or so, so this isn't normal!

I'm at work so I can't give you the exact water parameters, but they are all within sensible ranges. No ammonia, nitrite, small amount of nitrate.Temp is about 76 degrees. Tank size is 6x2x2.5. Water looks clear.

The dead fish are two 4" bristlenose plecs, a 6" clown loach and a 3" silver shark. No sign of disease or listlessness. All other fish are eating well and swimming around normally. Inhabitents are 8 silver dollars, 6 silver sharks (2 medium, 4 small), 4 baby bristlenose plecs, 1 large and 5 small clown loaches, 1 large cat-fish. The tank has a sand base layer and some big bits of bog wood. No vegetation (as the silvers dollars eat it).

On Monday I did a 60% water change (I generally do water changes of this size as it is a fairly long job anyway so might as well get it done). The water coming in came via hose from the tap (mixed hot and cold water). I kept an eye on the temperature to make sure there weren't big changes - adjusting the temperature as required. I added an appropriate amount of Prime before the water.

On Tuesday I added 5 small silver sharks - they seemed happy from the start. Thursday a plec was floating. Friday, one of the new silver sharks, Sunday the other plec. Today the large clown loach (my favourite ).

I rang up my fish shop and he said it probably wasn't the new fish - any disease would have been slower and with noticeable symptoms, and that it was probably the water change. I've been doing the water change like this for a year without any problems, but he said that sometimes the water companies put extra chemicals in the water that can kill off your bacteria if you change too much water at a time and that I shouldn't change more than 25% at a time. He said make sure you've got air bubbling through the tank (I've got an air pump), and add some Cycle to try and get the bacteria levels up.

So I guess my questions are
(1) Why are the fish dying - does the water change scenario above sound like the culprit?
(2) If the water change strategy is wrong, them how should I be doing it?
(3) Can I do anything to try and keep the other fish alive?

You get quite attached to the fish after seeing them grow for so long - any help would be greatly appreciated.

Cheers,
Matt

 

[leighton_87]

How are you dechlorinating the water?

Doubt this is a problem since its web fine for over a year but worth thinking about.

 

[Aquatious]

Hi - thanks for replying.

I've been added Seachem Prime to the tank before adding the new water.

 

[Chad]

Is there anything you can think of that might have lowered the oxygen content in lower part of the water column?

 

[Aquatious]

Unless I'm getting some kind of build up in the sand? The pleccies go quite high in the water anyway as they go right up the bogwood. I've had the water from the filters dropping into the water to try and oxygenate the water - loads of little bubbles in the water from this. The fish shop said that was probably not sensible as it may just be forcing "bad air" trapped under the glass back into the water...

I might try and get another air pump in just in case.

Would there be any symptoms of low oxygen? I haven't seen the fish gasping or sucking at the surface.

 

[Chad]

The fish shop said that was probably not sensible as it may just be forcing "bad air" trapped under the glass back into the water...

I've honestly never heard of anything like that.

The fish won't always gasp at the surface it really depends on the species and the fish. I'm not saying that is what happened but it's more common that people think. Maybe something along those lines.

 

[Aquatious]

Sounds like a sensible candidate.

I've got a powerhead moving the surface of the water and plenty of movement from that and the water coming in from the filters. Having said that the tank has 2 foot depth of water so maybe you are right and the fish in the lower part of the tank aren't getting enough. I have an air pump, but it does look pretty small and insignificant in the corner of the tank...

 

[Chad]

It's just odd for fish that are doing well to suddenly die. Now...because you said you hadn't had any fish die for a year I was assuming these fish had been in there for that amount of time or close to it...if they are recent additions then there might be other factors. It's just that when a tank is plugging along fine and then something happens the first thing I look for is changes in the tank environment.

 

[Aquatious]

Yes it does seem odd. I did add those 5 small silver sharks - but I can't really see them adding to the load on the bacteria enough to cause problems. Apart from those the rest have been in for a good long time.

Thinking about it I did add a new food this week - floating cichild pellets. I bought them for the other tank, but put them in by mistake into the big tank (no cichlids!). I left them in as the dollars seem to like picking food from the surface and I didn't think it would do any harm. I'm sure this wouldn't have had ill effects, but it is something different in the tank environment.

 

[Chad]

Sometimes the addition to the bioload plus the stress of having new fish around leads to quite a strain on existing occupants. Unless you saw clear signs of disease I think you're left with it being something that the new fish addition changed in the tank.

 

[Aquatious]

Thanks for the input.

I think I'll get another air pump for the other end of the tank, and perhaps cut down on their food a bit. If there's any uneaten food at the bottom then that's only going to make things worse.

Is it worth trying to get an oxygen testing kit to confirm if this is the problem?

 

[Chad]

I would say no. Since oxygen is such an important aspect of the tank (especially brought on by good surface agitation) as a general rule I say more is better. It's something I just go all out with in my tanks. It's tough for me when I use C02 on my plants because I have to remember that I can't have so much surface agitation.

 

[Aquatious]

I'd like to get some plants in my tank, but the dollars just woof them...

 

[Chad]

There might be a type they won't, worth exploring. In my marine tank I have a yellow tang which is a major algae eater. I like macro algae, it's like a plant for a reef tank, but the tang eats it. I have found that it won't eat halimeda so I can keep it in my display. Perhaps there's a plant out there that isn't palatable.

 

[Aquatious]

I got home and put an new air stone on and moved it closer to the bottom of the tank. Then I added some cycle in the tank. 850 litre tank - I had a small bottle that would treat 450 l, so I poured it in. As I did so (and I have no idea if connected or not - I have no idea), one of the big clown loaches started spinning round and round like a whirlwind at an incredible rate of knots not looking happy at all! I think he knocked himself out on the glass as he then dropped to the bottom and sat there looking dead. I gave him a little poke with a net, and he started swimming off but sometimes upside down and looking bad. He has now sat on his side on a bit of bogwood and is breathing heavily. He appears to have a sore on his side (small round red mark) but this could have been from where he was thrashing about. I'm very confused now and don't know what to do with him Any ideas?