I personally use the 5 gal Orange igloo water dispenser coolers. Keeps my res temp lower. You could use a regular chest type water cooler and use a net pot as a templates and jig saw some holes in the top for the net pots to sit. Doing this I top off res with milk jugs of water I had in fridge the night before and keeps my res nice and chilly till the next day. I found plastic buckets to get to hot and was using way to much ice to cool and maintain temps, slime was horrible. Every now and then I will throw a few handfuls of ice in there if I feel it's getting to warm. I found a ideal res temp to be key in any successful grow. I still use hydrogaurd to break down my carbs but not only does cool res help keep slime away, it is also important for O2 absorption.
Bakenast taught me everything I know....a true Midwest grow legend.