I'm NOT an experienced aquarist .. so I'm not sure I follow your setup ... I always use an internal thermometer set away from my heater and use it to set the heater at the temperature I want... in other words I ignore for the most part settings on the heater. The thermostat on your heater needs to be adjusted in small incements raised or lowered .. SLOWLY .. change it and wait until the tank temperature rises or lowers as it may be and stays steady... then change the thermostat again if need be otherwise you will be all over the place temperature wise ...( This you already know .. perhaps ? )

Keep in mind your setup is rather small so room conditions can have a larger effect compared to a larger tank but then again the water should be too cold ... it would seem ?

I have a 20 gallon and a 100 watt heater .. temperature stays right at 78 F maybe +/- .5 to sometimes 1 degree .. room temperature about 69 to 70 and the heater is not exactly top shelf. If I found the temp off 5 0r six degrees I'd too would be concerned.

Good Day ...

I haven't touched the settings on the heater in 3 weeks. Tonight the water went up to 86 degrees. But the heater has been off for a couple hours now and it's only gone down to 83; the house air temp is 72. I know that the Betta doesn't mind a temp of 86; I'm just afraid of how much hotter it can get.

WW

A couple suggestions...if the heater is too high...change the settings. Maybe I'm not understanding why you haven't turned it down yet? After all, I bet you'd turn down YOUR thermostat if your house got to 86 ;)

I have had lighting continue to raise temperatures even after the lights were off from remaining heat, but never enough to have an effect the next morning.

If you want to speed cooling, open the lid of the tank and set up a fan to blow over it. As the water evaporates it will cool. Your house temperature is higher than mine (67) so I'm not sure how much stronger an effect this will produce in a heater, especially in such a small tank.

The only other thing that comes to mind is the idea of the tank being near a heat source you haven't recognized, but that seems very unlikely. Good luck, I'm sure your betta is hardy enough to stick it out until you find a way to make that heater work!!

Kayleigh

Personally I use the heater settings as a guide only, and then set low and adjust from there to what my thermometer says. My heaters are all at least 4 degrees off from what the temp settings are, regardless of the brand. (I use a couple rena models and visitherm, horrible luck w/ ebo jaeger) Try using an old fashioned aquarium thremometer, as some externals are low quality.

If the room has ambient light, try leaving the compact flourescent off for a day or two and see how this affects the temp. Try the reverse also, light and no heater. If you find the light keeps your tank near 80 without the heater, put it on a 12-14 hr timer. The water will cool slowly over night, especially if you insulate the non-viewing sides with 1/4" styro painted black, dark green, or dark blue w/ acrylic paint. I would do this anyway as it helps keep the water from changing temp quickly (cutting down on electric bills) and the dark color makes the fish more secure than having clear viewing areas all around it.

If you find having the light off w/ the heater is the right thing, find a way to put space between the light and the tank. Having air space (even 1") between the tank and the light will help keep the light cooler. This is much better than evaporating the water to cool it. (which can wreak havoc on your house!)

Heaters that malfunction and are always on are a common problem with lower quality and old heaters. There is no question that a 25w heater can cook 4 gal of water, as I've gotten 5 gal up to 95 with one. (without fish in the tank)

Also keep in mind that the heater will over-heat the tank by about 2 degrees (in my experience) before shutting itself off. (It will turn on at 2-3 degrees lower than it's set) I would try setting the heater a little lower yet (bettas are comfy at 78) and see what happens. If it still ranges widly up to 85-ish, take it back and get a different one.
Nick

I would think that any higher heat above 80 degrees would be too much for your fish including your warm temp Betta. I have a 12 gallon Nano Cube glass Aquraium and keep the temp at 77 degrees. My male Betta and 2 female bettas are doing fine in the romance sense. The key goal is keeping temperature consistant. I have a submergible heater recommended my the fish store. (warning some cheap submergible heaters can explode) and I have a therometer that sticks to the side of the aquarium that works well and is consistant with the heater. You should not have a drastic change in your temperature, that would stress your fish. If it was me I would check out a better heater for the size of your tank with more control. It is better to pay a little more for peace of mind. Also in the long run, you end up saving by spending a little more for the better.
Theresa

Hi again
Well I found this bit of information about Temperature for Bettas...The temperature can be up to 90 degrees Fahrenheit. None of them sink to the bottom. They swim around and they eat well. They did not get sick. I find that Bettas get sick if they suddenly get chilled. I tell people to keep their Bettas in the warmest and quietest place in their home.
So I guess I should raise my temp to 80 degrees. I will do it slowly.
Theresa

Min temp for bettas is about 76-78, they come from shallow water in very warm areas, their water heats up cosiderably. While I don't recommend keeping bettas in 90F water, it's no problem. 80 is general maintenance and breeding temp, I raised young at 82-84. Temp swings should be slow, but a range of 6-8 degrees over a 10 or 12 hour period isn't a problem.
Nick

I'm pretty sure it's just the heater; it has gone up to 86 at night when the light wasn't on at all. I don't want to turn the light off because I have plants. I've been plugging it in for a couple hours when I see the temp get down to 78 or so and unplugging it when I leave for work. I'm working stupid hours right now, when things calm down I want to take the heater out of the water and see if there's anything obvious wrong with it; if not, I'll probably buy another one. Good to know it can heat that volume of water up that much; more incentive to be careful.

It's interesting to hear that they can be off by so many degrees, although I guess I shouldn't be surprised. For a while keeping it set at 77 kept the actual temp at 80; but now it's really fluctuating, as I said. Maybe it's normal, but it makes me nervous. The heater cost over $20 bucks: what do people consider 'cheap' for a heater?

Covering the back of the aquarium with styrofoam isn't a bad idea either, but would it bother the fish if I left it white? I'm trying to grow plants, too, and the ones in the back of the aquarium get little enough light as it is.

Thanks.

WW