stone fishDo whaleCave bat
Well first off 12 feeder goldfish in a 29gallon tank is way too many goldfish. That's where the problem lies; there are too many goldfish in the tank therefore they produce way more ammonia than the biological filter was ready for. What happened was the bacteria colony of nitrosomas grew and converted the ammonia into nitrite. Unfortunately the other type of bacteria; (nitrobacter) have not yet formed or were somehow killed off by salt or medications. This causes a spike in nitrite, here's what I recommend doing to lower the amount of nitrite in your aquarium:do severall large 50% water changes each day that the amount of nitrite stays highadd 1 tablespoon of aquarium salt per five gallons of water to prevent nitrite gill damage of the fishdo not feed the fish (goldfish can typically last a whole week without food before they begin to starve, one of the advantages of being "cold-blooded)Get a bigger tank! each fish needs a minmum of 10 gallons to thrive