LW

what type of pump and res volume? my 250GPH pump has a ceramic impellar...this thing barely makes a sound and uses very little electricity...using less electricity in a unit that is less likely to radiate heat simply means less heat added to the res unfortunately the pressure the impellar puts on the water still imparts some heat....different pumps could vary widely in temp change I can't say for the other pumps made but once again =>my<= 250gph pump runs 24/7 and it barely raises the 10 gallon res 5 degrees

A pump running 24/7 will last longer than one on a 60/15 schedule. Obviously the life of the pump is affected more the hotter the pump gets during operation...Doubling the life of your pump saves you the cost of replacement...if you still save more money in extra pump life compared to added electricity use and all other things are equal ie the plants will perform the same I would have a hard time turning the pump off...

If a plant absolutely needs dry time using a cheap electronic valve switcher rather than buying an interval timer for the pump might be the way to go with that you'd get the added benefit of 15 minutes of having the res mixed while extending pump life

I don't see how you can call myself or Jack, for that matter, careless when you didn't find out the specs of materials that were involved in our case study...I admit I probably should have been more specific (this post is to clarify) but you didn't even reference res size or pump rating in your comment...furthermore you said if water feels warm it's too warm...that's just too subjective for more reasons than I care to denote (if yer hellbent on that I'll reply later with a list)...just use a thermometer.

As for the 2" plywood subfloor suggestion...I know doyu didn't ask me but frankly I don't care because if its sole purpose is keeping res temp up that's just a bad idea for so many reasons...material, labor, the fact that non pressure treated wood wicks?sp? moisture which would increase the rate at which temp would be tranfered which would greatly reduce effectiveness of the resolution, not to mention the nasty mold issue depending on severity of moisture leak from the slab and it wouldn't do nearly as well as several thin styrafoam?sp? sheets which are much cheaper, easier to install and even give you some ability to control res temp increase in several stages ie removing/adding layers...

All that being said...

doyu, you should look at the watts of your pump and compare that to the watts of same gph rated pumps...it might actually save you money to buy a different pump and junk the old one...lowering overal res temp is just a bonus...if it did come down to running pipes along the slab I'd just drill holes in the bottom of your res and make a metal heat sink that would sit between the res and slab with in effect radiating metal in the res to cool it off this solution would probably be quicker and way more stealthy than pipes snaking around