We can't give exact numbers because it depends on the animals you are keeping, how quickly the swing in temperature happens, and also the accuracy of whatever device you are using to measure temperature could be off by a couple degrees potentially too.

If you are getting anything over 80, and it is a hot day and potentially getting hotter, I would play it safe and throw in a couple of frozen pop bottles. If your tank temp drops too much, your heaters will kick in. And install fans if you haven't already.

I wouldn't let it go higher than 83. 86 at the absolute highest.

If possible keep it within 3 degrees of your current temperature. Ocean temps do not change more than 1 degree a day apparently, so we should try to aim for stability. Any time you bring your temp down you won't want to do it too quick.

I've got my lights on a reverse cycle over the summer. They come on at 2am and go out at 10am. Actinics are on from 6-12 so that I can see the tank when I'm home from work. This way the hot MH lights are on at the coolest part of the day. My temp range is 77-80 using this method. So far, I haven't needed to use any other method to cool the tank.

You can also use fans, small water changes, and clean pop bottles of frozen RO to chill it. I've considered frozen cubes of Ro water for top off... holding it in the tank and letting it dissolve cube by cube.

I have heard of tanks hitting 85 for a while without any ill effects, so 86 sounds like a decent "max".

Anything over 80 and I would panic, because my tank temp doesn't ever go over 78.

This morning my tank was only 77.1 I still have no heater or livestock in my tank so it really does not matter what it goes to, but I would rather it be too cold than too warm

My tank has been fluctuating between 82 in the morning and 84 in the evening. Normal temp is 78-81. No ill effects yet... other then corals growing very quickly :mrgreen:

I have heard of one tank fluctuating between 79-89 everyday..

I generally have it at 79F

However today it hit 93F ... good thing my tank is still cycling. Time to break out the fans!!! I can't afford a chiller ... Any other thunks besides dechlorinated water ice cubes?

Fill your empty milk jugs and freeze them. If you can fit this in your sump your good to go.. :mrgreen:

if your tank is still cycling, and you have no livestock/corals, I'd just turn your lights off for a few days until the heat passes, put a fan over your tank...

If this isn't a solution for you and you live somewhere where heat is abig problem.. and a chiller isn't affordable for you, you might want to consider coming back into the hobby when you can afford a chiller, simply because you have so much more to overcome you need to be more prepared than most.

oh yeah, and if your tank is cycling and you DO have livestock in your tank. Shame on you!

Well, i figured out that it was my lights. Have to cool the air between the lights and the water now ... i thought there was enough air flow but i guess not.

i friend of mine lost a lunar wrass on wensday, his tank was at 87.5 when he got home after work.

My tank is hitting 86 no problem right now. I'm going to have to cut back the lighting period big time... but , everything is doing great and no signs of stress on anything (yet.. )

Well, it is now 1.5hours after my hallides turned off on a moderately hot day (compared to the last few and what I'm sure will come) and I'm now at 86F. I'm getting pretty antsy to get a chiller for the tank, but when I look on the net to see prices, it almost seems like a better idea to get AC for the house instead. I REALLY hope I don't lose anything due to the temp... that would suck.

I think it's wise to cut back on your lighting on hot days. Also, when I come home from work I check the temp and if it's 86, i'll take a ziplock baggy filled with ice cubes and put it on the water surface. I usually need 2 baggies. This usually brings the temp down nice and slow, so it's not a big sudden change.

I picked up a little a/c unit from Rona. Now the tank stays at a steady 81 like normal.

I just installed a digital titanium heater and probe set-up. I was shocked when I hooked it up yesterday to see my tank was at 29.7C. I have since taken out the old heaters and the tank has cooled to 27C, I am shooting for 26C(78F). My old heater was actually on and hot when I took it out so I am glad I made the change. I had also been using a 25 year old thermometer left from my cichlid days as well which I discovered was inaccurate too. It's a real shame when you have some cheap piece of equipment ruin the thousands of $$ invested. I decided to spend a little extra and hopefully save a lot later. Maybe this can help explain the RTN and brown out problems I have had with my sps of late.

So, I come home on wed. to find my corals all shrivelled and dead looking.... look at the temp to find it's at 94!!! Somewhere between 89 and 94 is apparently the death point. At 89 this were ok. I lost my favorite: 15+ head revearse colour hammer, my frogspawn, possibly some leathers... they may come back...??? a starfish and 3 brand new cleaner shrimp. VERY MAD!!!!! I love the heat outside, but STAY THE HELL OUTTA MY HOUSE!!!!!

With one fan on during moderately hot days & up to three on the hottest days, my groundfloor suite is great because the tank temp has stayed 80F or lower. Before I plugged in the fans, it reached a high of 84F, but that was my fault since I also had the window closed.

Anthony