It's a bit late now, but you don't really have a choice; you have to vacuum until you get all the food out. Change the water 20x if you have to. Make sure you wash all the food out of the filter too, preferably with dechlorinated same-temperature water to save as much of the biofilter as possible.
Don't worry about saving any old water... the fish will not thank you for saving the water that had fish food soaking in it overnight. A spoonful of rotting fishfood will kill more fish than 100 buckets of fresh clean water will. If you do regular water changes, big water changes are nice for fish, not dangerous. In this situation, new vs. old water is the least of your problems.
The tank is likely to be a bit unstable for a while afterwards; it would be a good idea to keep a close eye on ammonia/nitrites for a couple weeks and do more large water changes if necessary.
If you use simple dechlorinated tap water in your tanks, it's very easy. If you use pH adjusters or otherwise make the water different, it's more work, but it needs to be done. Hope everyone survived so far.
Don't worry about saving any old water... the fish will not thank you for saving the water that had fish food soaking in it overnight. A spoonful of rotting fishfood will kill more fish than 100 buckets of fresh clean water will. If you do regular water changes, big water changes are nice for fish, not dangerous. In this situation, new vs. old water is the least of your problems.
The tank is likely to be a bit unstable for a while afterwards; it would be a good idea to keep a close eye on ammonia/nitrites for a couple weeks and do more large water changes if necessary.
If you use simple dechlorinated tap water in your tanks, it's very easy. If you use pH adjusters or otherwise make the water different, it's more work, but it needs to be done. Hope everyone survived so far.