Of course it is hopeful! It is odd how a fish in deplorable conditions from a tank that hasn't had water changed in months a fish can survive and in another the slightest change and all heck breaks loose. Fact is that the little guys are already survivors and also don't be too alarmed if any perish as the strongest survive, it is just a fact that some are too weak to live a full life. It is natural. Just make sure to keep good water parameters and do frequent pwc
. New life is fun to watch.
For the filter, you can add a sponge over the intake. There are some from Fluval for the Edge tanks and they will fit on most intakes with a little gentle pulling if it is a larger diameter. I have used panty hose knee highs too with a double rubber band in case one fails. Just rinse well and use a new one.