Water temp, Cooling fans and evaporation


New member
My temp would drift between 81 and 83. It didnt matter if I had the MHs on for 6 hours or 12 hours. I didn't have the glass lids on either.

Here's what I've got on a 90g tank.
1 x MJ1200
2 x 250W MH
4 x 65W CF Actinic
1 x Corallife SS65
1 x Mag7
2 x 26W CF over sump

I also have a 200W Rena heater set on 76F. With everything I have on there should my temp have been that high? I.e. is something not working right?

I took a little 6" fan and wedge it between the tank and the wall to blow over the water surface and it brought the temp down to 78-79 over a period of about 5 days.

Only now I am evaporating somewhere between 1.5-2 gallons a day. Is that typical?

What experiences to others have with evap?

I bring home 2 gallons of DI from work every day and I'm just keeping up. Over the weekend the level in my sump is sure to get low.

I'm sure the overwhelming response is going to be .... get a chiller.


COMAS Rocks!
I think it's okay. 81-83 isn't really that bad, if it's stable there. I wouldn't go any higher if you could avoid it. A chiller would allow more margin for error here. My temp gets about 81 during peak daylight hours and I too use a fan to cool it down. The temp sounds typical for that size tank with that type of equipment running. MH's can add a bit of heat, and the powerheads add a tad, return pumps can add a little. It all adds up. that and you have to consider ambient room temperature. My tank sits in a room that never goes above 77. Got a window A/C sitting about 6" from the tank and even with the ambient temp that low, my tank willreach much higher temps. 2g evap doesn't seem to excessive. My 55g evaps almost 4 "subway" cups a day. (I forget what size there large cups are, but that's what I use :D) But I'm only using T5's which do run alot cooler than MH's do.


New member
Double check your heater. I had a heater set on 72F and my tank kept creaping higher and higher. When it was new it kept things right between 77 and 79F. Finally pulled it, and did an emergency water change when I got home from work and the temp had gone up from 79F to almost 87F in five hours. Put a little stress on my corals but they have all recovered, thank goodness!!! May not be your heater, but it couldn't hurt to check.

Village Idiot

New member
My temp stays at a steady 80, with no cooling fans blowing on the water and no chiller. I researched and choose equipment that would not add a lot of heat to my system (I also run a dual 250 watt MH fixture with actinics). You will pay more to do this...pay me now, or pay me later, but your gonna' pay!

Your evap rate seems to be about what mine is...I added an ATO so I can leave the tank alone for a week or so (longer with a larger reservoir)


New member
81-83 is not that bad. 1.5 to 2 gallons a day is normal in my 90. I have a fan built into my lights and an 8 inch fan that blows over the sump (all on a timer).

amosgirl is right about the heater. I have yet to buy a heater where the number on the dial actually heats to the correct temp. When I setup my 90, I ran it a week with no lights to make sure both the heaters were dialed in properly...


New member
I'm glad to know that 81-83 isn't so bad. THe tank sits close enough to a window that its does get some direct sunlight and on particularly sunning days it would push the temp up to 84.

I'll probably switch to running the extra fan when the MHs are on. Although I'm thinking about adding an extra powerhead or two so I'll have to see once I do that.

I may unplug the heater and see what happens over a few days.