We have a plagued 5 gallon tank. Story follows, but main question is the following: After stripping a combo of fry and eggs, all the fry have died. Don't know why (more on that below). We moved the eggs to the display tank where we knew the water would be safe (did not move any water to avoid any cross contamination). Is it worth giving them a shot to hatch? Or would the eggs be more delicate than the fry such that they are unlikely to make it? The tank the fry were in was initially used as hospital tank for one sick adult fish, dosed with erythro, fish died. Cleaned (water only) and tank idled dry for weeks. About a month ago, stripped about 30 demasoni fry into it. Fry died in under 24 hours. We caught it with 8-10 dead, changed water, and when fish kept dying we moved them to another tank. 100% mortality within hours. We guessed we overdosed the nitrifying bacteria, caused algae bloom, algae used all the oxygen and damage to fish was done before we got home and started trying to fix it. Huge bummer. Cleaned (water only) and tank idled dry for the last 3-4 weeks. Sunday we stripped some eggs into a tumbler and some fry into the tank. Again washed it out with water before using it. Set it up 24 hours beforehand. Running with sponge filter from a seasoned tank. No nitrifying this time, so oxygen levels should have been fine. In a day and a half, again dead fry. We got a few of the still-feisty ones into another tank this morning and will see if they make it. Based on last time, I don't expect them to. As I mentioned, the tumbler is also in another tank now. The solution here is easy enough, get rid of the tank, buy new food and don't look back. New 5 or 10gall and some NLS fry starter aren't a big investment to not lose any more fish. Of course I'm wracking my brain as to what is going wrong though: - Biological contaminant seems unlikely -- I'm sure there is some crazy organism out there that can survive as much washing as we did, and being dried out multiple times, but feels like long odds. - Chemical contaminant -- something got in there somehow. This was my gut because it just seems like limited other explanation. Might explain why it took longer this time to start killing fish: diluted by last round of cleaning. Worth nothing, we got the tank from ACA, so show fish lived in it for a short period of time (i.e. probably not anything leaching from the tank itself). Adult fish were in it for a short time while stripping with no obvious ill effects. - Water quality -- despite seasoned filter, ammonia tested 0.5ppm this morning. At our pH and temp, even for fry, seems like it shouldn't kill them outright in that amount of time. - Food is bad. I don't see a date on the container. We probably bought it a year or so ago, but who knows how long it was on a shelf before that. - Other??? I'm happy to give the eggs some time to see what happens, unless it's pointless. The solution is clear for next time. But, anything else I need to learn here?