• Gabriel

Karen81

Do the tests, turn on the skimmer for wet foam (thinner), replace it with a 30% water change. Depending on the equipment, use a good sorbent to remove organics and phosphates from the water. Find all the dead ones - remove them. And do this for 3 water changes - every 3-4 days. Maybe someone else will correct or suggest something! Hang in there!

Antonio

If I understood correctly that the aquarium is 40 liters, I would find some live water and a container of suitable size, transfer the fish and all living things there without stones and sand, and put a filter with a sponge in it. (Because in three days, the sand and stones could die from lack of O2.) In the aquarium, at that time, you should do a review, a water change, and tests for ammonia, nitrite, and nitrate; they should indicate the condition of the aquarium.

Amanda

Urgently change the water; if there's no source, prepare fresh water. I would change 70-80%. The fish should be removed separately, as mentioned. The sand and stones apparently release ammonia abundantly, which is understandable, but within a couple of days, everything should be processed into nitrates. Action should have been taken within the first day; I hope the light has been restored.