Backyard Aquaponics
A place to discuss aquaponics

The short answer is yes. I no longer think ammonia, nitrite or pH were at fault. However, the one common unusual feature was that acid rather than alkali addition was needed to control pH at the time of the fatalities. However, this is still the case with the new fish and may just indicate in their case that they aren't producing enough waste for the system pH to trend downwards.

The long answer is...Yes, but situations were different. In the first case, the 100x 150g silver perch were added to a 1000 litre tank that had only been cycled with the help of ammonium sulphate and a few goldfish and koi. As a consequence, the biofilter struggled a bit. pH waw controlled around 7.0 to 7.3 but TAN reached as high as 0.25 and nitrite as high as 0.5 intermittently over the nexrt month. The system was then hooked up to the polyhouse trough which had the "stagnant" 3-week old water in it. TAN now remained between 0->0.25. Intermittently nitrite veered above this level as high as 0.5. The fish started to die three days after this change and this continued for a week. pH was rising rather than falling through period necessitating acid addition. As *I said before, I think the problem was overcome largely by several large water changes.

In the more recent case, the water in the tank was cycled for about three weeks and the biofilters recommissioioned with some seeding with ammonium sulphate.Water was TAN=0->0.25, nitrite= 0, pH 7.6 at the time fish were added. Again acid additions were needed to control pH around 7.4. Some of the small fish started dying after 5 days. The problem this time was rectified with water change, salt addition and water heating.