CLR? I had to look that up. A seriously gnarly household cleaner it looks like...
ingredients consist of: GLYCOLIC ACID, DISODIUM CAPRYLOAMPHODIPROPIONATE, SULFAMIC ACID, 2-BUTOXY-ETHANOL, 2-HYDROXY- 1,2,3-PROPANETRICARBOXYLIC ACID, and water.
Yummy! LoL I guess it probably works heheh. Make sure you rinse the fuck outta that baby though... Everything leaves residue. Personally I think I'll stick with my bio-green clean & pressure washer idea
That bio green clean dissolves salts and algae better than any other cleaner I've tried, although I haven't tried CLR...
You bring up a good point about sizing though, that I forgot to mention. Pay no attention to the gallon ratings for aquariums that these chillers have... You want to pay attention to horsepower and BTU's. Usually a "300-500 gallon" rated 1/2 HP 6000 BTU chiller is only able to handle a 100 gallon hydro reservoir tops. It really depends on how much cooling you need though. Some people might be able to get away with a smaller chiller on a 100 gallon reservoir if they only need a few degrees drop, others might need a 3/4 HP to cool that size of a reservoir if they need say 15-20 degrees drop.
for a 40 gallon reservoir I'd recommend at least a a 1/3 HP. For 20 gallons a 1/10th HP is probably fine. Oversizing is always better, as it will make your chiller last longer because it wont have to run as often.