Water temp rising

[howmanyds]

I just added a second Hydor 300w inline water heater to my canister filters on my 75g. a few days ago. Strangely, over the course of a few days, the water temp has risen from 80, where the heaters are set (for African cichlids), to 83.5. Yesterday I unplugged the older Hydor, thinking it might be acting up. But this morning the temp had still risen two tenths from the night before. So I unplugged the second newer heater four hours ago. The room temp is about 80.

First, how do I safely get the temp of the tank back to 80? I need to do a water change today but don't want to shock the fish.

Second, what else could be causing the temp rise?

The only other change was adding some crushed coral to my filters about 5 days ago.

 

[Berylla]

Is your heater set to the lowest setting? If yes, then your heater's wattage is too high for your tank.

 

[howmanyds]

The heaters are unplugged right now while I wait for the temp to drop back down.

They were both set to 80 degrees. They have internal thermostats that are supposed to activate them when the water temp gets lower than the set temp. And, obviously, they're supposed to not heat water that is already at 80 degrees.

 

[Berylla]

Heaters are not "perfect" and will never get the temps exactly right. If you would like absolute control, get a temperature controller like this one:

Finnex Deluxe Electronic Temperature Controller - AquaCave.com

I've been meaning to buy one for my discus tank just in case my heater goes nuts on me.

 

[howmanyds]

Those only work with the heating rods in tank, correct?

 

[Berylla]

Yes, that's my understanding of how they work - you plug the heaters in the device and the device has a thermometer that raises and lowers the current to power the heaters.

 

[howmanyds]

My bigger concern than the heaters right now is:

Why is my water temp rising while the heaters are unplugged??

This afternoon at 4:00 I did a PWC bringing the temp down from 83.5 to 82.8. By 8:00 the temp was back up to 83.1. The room temp is still 80.

What could be causing this?

 

[Berylla]

Oh I see. What filter are your running? What other are you using in your tank.

 

[howmanyds]

I have two sunsun 303b canisters filled with (from bottom to top): sponge/floss, crushed coral, sponge floss, bio-balls, seachem matrix, purigen.

My light is an LED so I don't think it's adding any heat.

Could too much feeding be causing heating?

 

[Berylla]

I have two sunsun 303b canisters filled with (from bottom to top): sponge/floss, crushed coral, sponge floss, bio-balls, seachem matrix, purigen.

My light is an LED so I don't think it's adding any heat.

Could too much feeding be causing heating?

Food will not cause a jump in temperature. HMMM. Are you running a UV? Any UV, even the ones that are in your cannister filters run hot and will change the water temps.

 

[howmanyds]

Yes. The canisters each have UV lamps.

What are they good for?
Should I just switch them off?

 

[Berylla]

Yes. The canisters each have UV lamps.

What are they good for?
Should I just switch them off?

If it's 5 to 9 watts, it's good for green water or cloudy water. It will not kill pathogens or parasites. I would switch both off for now, and see if your temps drop. I use a 15 watt UV in my tank but I like my temps high because of my discus.