Loaches Online Forum

I've had a 200L hillstream tank set up for nearly a year, yesterday I noticed some of the fish breathing rather heavily, they all looked healthy and were eating well I decided to change 1/3 of the water as a precaution.

The tank has 2 eheim external filters and 1 internal power filter which blows oxygen too, every night the oxygen is turned off because the tank is in a bed room. This morning I woke up and noticed the barbs in there gasping at the surface, turned on the lights and found the following fish all dead, 3 x Sewellia lineolata, 3 x Gastromyzon scitulus, 2 x P cheni, 2 x Garra ceylonensis.

I can't find what could have caused this there are no signs of illness in the fish, and water quality doesn't seem to be a problem, temp 23 degrees, ph 7.5, kh 9, gh 12, ammonia <0.1mg/l, nitrite 0.1-0.2mg/l.

any ideas what could have caused these deaths?

sorry to hear that. thats terrible!

when you did the water change, did you wash out the sponges in any filters? your water isnt quite perfect, there should be 0 ammonia and nitrite. perhaps the water change knocked the tank into a small cycle.

was the fresh water matched to the tank water? do y ou normally do water changes that size, or smaller ones? anything different at all?

is it possible that something got into the water to poison it, or remove available oxygen? something from dirty hands, or fumes from something you were doing in the room - painting, spraying lots of perfume/deodorant etc?

The parameter of the tap water is a good match to the tank water kh and gh maybe a degree or two lower, ph is the same. I usually change 1/4-1/3 of the tank water every weekend I did an extra 1/3 change on thurs morning cause I thought there must be something up. I havn't cleaned the filters for a month or so.

What really puzzles me is that after I changed the water on thursday they soon stopped breathing heavily and look just like mornal for the rest of the day and all fed well, then this morning half the occupants are dead.

I can only think some thing must have got in to the water like you mentioned but what I don't know, deodorant is only spayed in the bath room the other end of the house, and no cleaning product were used since last weekend.

that is really weird.

could any of your family/friends accidently done something and not told you/done something or used something without realising it was wrong?

how are the barbs doing?

What about your local water supply?
You might want to call the local water treatment plant and ask them if they added anything or did anything out of the ordinary on the days in question. Possibly added or increased the use of choramines? Its a long shot, but worth checking.

Just tossing out some thoughts. Really frustrating when something like this happens.

When you did a water change and they quit breathing heavily that does suggest there was something in the water that was bothering them.
When the water change (new) water got mixed with the old then whatever it was had been reduced enough to not be toxic for a while. Maybe there was something in the substrate that was temporarily diluted with the water change, then more of it got dissolved?

I have had this happen a couple of times.
I have enough tanks that I can usually grab all the fish out of the affected tank and distribute them among the other tanks. Yes, it is a risk in case it is a disease or parasite, but fish in suddenly toxic water do not look the same as fish with diseases or parasites.
Then I can do a couple of 100% water changes including REALLY stirring up the substrate. Refill, and I will use a dechlor that also locks up heavy metals, and add a lot of fresh activated carbon to the filter. Then repeat the next day, fresh carbon again. Then I will try a few test fish. (Usually Guppies, but whatever has been reproducing the most)

If I suspect lack of oxygen, but no other issues, then I will add 3% hydrogen peroxide to the tank @ 1 teaspoon per gallon. (5 ml per 4 liters) and increase the aeration, as well as fixing whatever quit and caused the poor water flow.

All the other fish thankfully seem to be fine now.
What also puzzles me is the fish that died all the hillsteam loaches died other than 1 tiny G. zebrinus and all 4 of my Homaloptera orthogoniata/confuzona, there are also verious gobies in the tank all of which like high oxygen levels and non of these died.

Diana, I think you may be right with your idea of there being something in the substrate the male Stiphodon most days will dig a burrow under a rock its allways the same rock, so he may have sturred up something toxic.