Urgent Advice Required!
11 days ago I had the misfortune of discovering what no aeration to a tank overnight does to fish. After playing around with my pump I forgot to switch the power back on. The next morning 29 dead barra Av size 18cm. Up until then the fish had been thriving. They were purchased as 10cm fingerlings 6wks previously and were feeding and growing rapidly.
My set up consists of a 500L tank supporting 2 growbeds. The water parameters currently are ammonia 0, nitrites 0, nitrates 20-40, pH 7.4. Temp 28-30
9 Days ago I purchased another 35 barra. These were slightly smaller about 6-8cm long. These barra were not as flightly as the 1st batch. Since then I have lost 8 (3 today) and at least another 4 are exhibiting the same initial signs. The fish (normally not more than 4) rather than spending most of the time at the bottom of the tank tend to swim close to the surface. At feeding they nudge at the pellets but have no appetite. They then tend to swim more weakly, sometimes being pushed around by the current and end up on their side and then dying.
The oxygenation in the system is the same as the previous batch (with fish over double the size of these fish) with loads of bypass water from the 3750L pump, plus auto syphons every 20mins plus a small aerator running constantly.
I just don't know what is occuring. I have added another aerator this pm.
If oxygenation is a problem do fish recover? and should I see an improvement.
Any thoughts on what is going on. Some fish are behaving normally as the last batch.
Any advice would be great