You don't want to leave uneaten food in the tank for that long as it degrades the water quality. If they are not eating it within a few minutes, it means either they don't like what you are feeding, the food may have gone bad or the water is not satisfactory for their health. You need to check all those things out. Try a different food or food type. Have your water tested. Do water changes if appropriate, etc.
Hope this helps.
The red racers shouldn't need the extra food if you have enough biofilm or algae in the tank. The shrimp may be eating leftover foods that are hidden among the substrate. Have you tried foods that are Algae based like spirulina flakes or pellets? Have you tried sheets of Nori algae?
Personally, I don't usually feed my snails because that encourages them to keep up with the biofilm and algae growth. From what I've been reading about the shrimps, a lot of people use the Nori strips for their shrimps because it also contains calcium as well as a lot of micronutrients which the shrimps need for their shell creation and overall health. Either.
Spirulina is the main algae in many algae based dried foods ( flakes, pellets, blocks, etc). You might want to try some spirulina flakes along with the Nori strips. ( I also read that the shrimps don't all rush over to the Nori but over time, they find it and you will see them on and eating the strips. )
)Feed the flakes sparingly so that if they don't get eaten, they don't pollute the water. With the nori strip, again, uses a small piece ( maybe 2" x2" ) and feed that in the morning. If it is not gone by the end of the day, I'd remove it. If the shrimp do not eat it, I'd try putting it in about an hour before lights out and then remove what's left in the morning. ( It might be easier to use a veggie clip for aquariums to hold the nori so that you will know if it got eaten or not and it's not hiding somewhere in a hole in the decor.
