Tropical Fish Forums

[sensor97]

I have an outside pond tank - this is Hong Kong, temp rarely falls below 10*C and I have a heater set at 24*C in there to create a warm area if the temperature does fall.
I had two Plecos, about 4 years old, and growing well, (about 20+cm). A big recurrent summer algae problem led me to get a power filter, and I put activated bacterial rings, activated carbon and foam/filter wool inside as per instructions, washed it all through with "old water" and set it going.
Within 48 hours, my Plecos were dead. There was plenty of glass covered with algae for them, and indeed the power filter didn't fully solve the problem, but at least I could now see the other fish, all of which remained healthy. I put it down to their size, despite daily feeds for the other fish, which they stole liberally.
I bought two 7cm Plecos, acclimatised them in the oxy-bag for about 6 hours, and let them loose. Within 48 hours they were dead too. Can anyone think of why this should be - all the other mixed tropicals in the tank remained fine. I have not bought more plecos, but would like to, they are fascinating fish. Why should the mere addition of a power filter create an environment toxic to plecos when everything else is thriving?
Any suggestions very much welcome, solutions to allow me to have pleco's again, even more so.
Many thanks.

[diademhill]

I really need a bit more info but a couple of things come to mind so far...

Temperature - if the heater was providing a warm spot the filter would prevent this happening.

If there was no filtration before the filter will have moved detritus & released trapped gasses.

4 year old 20cm plecos of common species are stunted.

How big is this pond? What fish are in it?

[susankatomerit]

That is pretty small for a 4 year old pleco, especially if its a common. Sounds like what was said, if there wasn't a filter in it to begin with it probably stirred up some noxious waste from the bottom.

Here is a pic of my 3 year old


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[sensor97]

Thanks for replies. The gases idea seems most likely, but why only the Plecos died, the other fish were fine - sorry for the heater red herring, it wasn't in a cold month, but you are right for sure, the hot spot would go with a filter, didn't think of that!! Perhaps 20cm was conservative, they looked about like the one in the picture posted. The tank is 80x88x10cm, about 75 litres with the external filter.
So maybe cautiously try a new small pleco with the stabilised set up - they certainly do have personality, and do a great glass cleaning job!