Sudden Deaths !

[louise.storey]

Help!
Woke up this morning to find all my fish lying on the bottom of the tank, hardly moving but upright.  Dosed with esha 2000 as thought it was the shimmies. went out and returned home a few hours later to find my 2 mollies dead, 2 platys halfway there and the remaining 4 danios looking skinny and on the bottom.  did a 50% water change as emergency, no difference.
 
water reads as follows
ammonia 0, nitrate 0, nitrate 0, kh 100
the temperature 24 and ph 8
50 litre tank no new arrivals for months.
 
however did put new heater in 2 days ago which was 150watt (too high wattage but local pet shop assured me it wouldnt overheat tank and would still cut out at required heat)  could this have done it i am stumped.  no marks on any fish 
 

 

[snazy]

That's odd. Sorry about your fish.

Try exchanging the heater if you can just in case, they can cause similar issues if faulty.

Additionally, first reaction would be a large water change, not adding meds.

 

[coolie]

What was the temperature reading?

 

[louise.storey]

temperature 24.  3 hours since 50% water change and no difference really, 1 danio is swimming about but all others on bottom.  dont think i can return heater as it works and was maintaining 24 degrees just wondered if it was responsible . will have to see what happens overnight i cant do much more tonight. thanks for helping

 

[snazy]

It could have a short. I'd suggest switching off/removing the heater to test and do a large water change and wait. That's presumed your room temp is not too low this time of the year to drop the tank temp considerably. If that's the only change you did it's worth a shot.