that's what they have been under. i changed the water the other day and the ppm's were up around 1500 and i let it go like that for a couple of days until i started seeing burn places around the edges so i backed it down to 1000 and she seems to be doing great. i'll never go back to dirt growing except outside growing.
you've got to find an aquarium shop. the ones i go to have a used section and you can usually find a 1/4 h.p. for a couple of hundred or so. something else to think about is going to a salvage yard and finding an old water drinking fountain
check out the ph monitors and controllers while you're there, i've seen them for dirt cheap before i was growing and didn't realize how sweet it would be to have it.
Yep you can find them at most aquarium stores where they sell exotic fish and what not. Be looking to drop 500 brand new or more.. Craigslist has them too but you know how flaky people can be on those sites.. Or you can go the cooler route use a Igloo brand ice chest or a igloo 5 gallon sport coolers ( 20 bucks ) and you wont have to worry about reservoir temp issues..
i'm using an ice chest for a resivoir and a 27 gallon tote for the grow bucket. when i had dirt plants in this same closet i was getting over a pound, sometimes almost 2. so investing in a water chiller is well worth the return. set it and forget it.