what's up man, yeah I don't know much about rdwc, I I think the water pump might actually warm the water up like you were thinking, unless a chiller is not something that cools the water...

Thanks for the reply Stumpy. I'm convinced the pump has to be the only difference. A chiller is not an option for me, the size of my grows don't allow for that. I've got a backround in computer overclocking and have extensive experience in water cooling and used to build refrigerated cooling systems for pc's, some of them were exactly like the chillers for hydro. I could build a 1/4hp chiller for less than $100, just don't want the extra wattage that could be going to better lights. I think I'll try a small RDWC without a chiller just to see how it goes, I've got a couple of ideas that should allow me to run without a chiller and not have res temp problems.

In my case, I had 7k of hid heaters raising the water temps, even keeping the room at 80 degrees, the res water is getting hotter and the pumps are bigger too, plus it's a submersible, so there's a couple of reasons for hotter res temps. I always prefer sterile rdwc, so if you try un-chilled, go with lot's of h2o2 or some alternative.

Hey 40brix, I can see where a chiller would be necessary for a grow like you have. I'm not doing anything on the scale you are. I run 2 600w hps in a 4X8 room and my room temps are usually in the low to mid 70's with air cooled hoods. I may just setup a little test system with one of my computer cooling pumps and see if I can keep the water at very close to ambient temp.

If your thinking of getting into RDWC a chiller is a must! go as large as you can afford!

A very knowledgeable farmer by the name of @ttystikk has multiple posts and discussions on the utilization of chillers and heat sinks ( ice boxes ) to cool multiple rooms and reservoirs. I would recommend reading everything in his profile. SO much good info. I use a 2 ton chiller as a complete environmental control for 3 separate rooms ( 2 with 4000W+ HID air cooled, 1 with a 600W MH open hood and a couple banks of T-5s) as well as cooling for mulitple RDWC systems. I also implemented his waterfall technique and was able to eliminate all air lines and stones. the girls love it. waterfalls sound awesome!

Live res with a bag of lava rock in epicenter to "colonize" bacteria from ewc/beneficial tea. Constantly adding h202 or UCRoots is laborious and in my experience only a temporary fix to what could be a very volitile situation. @Capulator beneficial tea once a week, never look back.

other contributing factors to water temps in RDWC ..
-quality of insulation on buckets, or lack of
-air pump is pulling air from inside hot room and into your buckets
-direct light from HID on buckets
-filter is clogged causing slower recirculation and decreased contact to cooled coil in epicenter.