Shorty once your filter gets established you shouldn't have to do more than a 10 percent water change per day which shouldn't drop your temp too much.
OTOH, have you considered letting make up water stand for a while in a separate container to get the temperature up?
I will soon have two makeshift iron filters which also warm up the water at the same time. The one I am using now is two barrels side by side with one stuffed with bunched up deer fence netting and filter pads.
The water is pulled up through the filter material via a pump that rests on top of the material in one tank which takes the water to the adjacent tank that lacks filter material. It then gets pulled back up a u tube siphon tube back to the bottom of the filter material in the other tank. Once you get enough iron build up in the filter material the filter works even better. At it's peak I can produce 50 gallons of crystal clear make water in 24 hrs.
The last time I ignored the iron it built up and caked terribly on my RBC.
Last edited by Cecil Baird1; 07/20/12 12:08 AM.
