Fish Tank Heaters?

Question

I've had some problems with one of my tank, and any time I plug the fish tank heater in, the tank always sits at a constant 80 degrees (with it on the lowest setting), according to two different thermometers. Here recently I've had to separate two of my mollies from the other fish as they where way too aggressive for the other fish in the tank (Strange I know). So I started a 10 gallon tank using gravel and water from my larger tank.

Thinking it was my cheap heater causing the tank to be 80 degrees all the time, I bought two new heaters.

So now I have a:

20 Gallon tank w/ 50 gallon filter, and 150 watt heater.
10 Gallon tank w/ 50 gallon filter, and 150 watt heater.

Both have a separate 30 gallon air pump with two large air stones in each tank.

The 10 gallon tank is perfect with, it sits at a constant 75 degrees.

The 20 gallon tank though for some reason has weird hot and cool spots, the front top of the tank tends to be 80 degrees, the back half of the tank is colder, .....

the back half of the 20 gallon tends to be more around 70-72 degrees. The heater is in the back of the tank, and I'm guessing thats the reason it's on so much.

Is this normal? I'm guessing its a water circulation problem? As I mentioned I have a very large filter on the thing, I would think that would be enough to circulate the water?

Would adding a water jet help? If I should add is just having it near the top sufficient?

My thermometers are just cheapo units, they aren't the stick on type though, they are a real thermometer, they both read the same when you get them near each other, so I'm going to assume they are fairly accurate?

Are the heaters pre-calibrated? I was reading the instructions and it said to let the heater sit in the tank for at least 15 minutes before plugging it in. The one in the 10 gallon tank did sit in the tank for that much time, while I was messing with the 20 gallon tank. The 20 gallon heater was only in there for a few minutes before I plugged it in. Would this affect anything?

The heaters are just the kind with the knob that goes + to -, no actual temps on the knob. The knob is in deed at the - side.

Answer 1

The larger the tank, the harder it is to keep a constant and consistent temperature throughout the tank. You may want to experiment with heater vs filter placement. In every tank, water flow is different (depending on rock, logs, and plant placement, and where the water comes in and goes out). In most cases, the heater element should be situated in the main flow (usually where the fresh water is going into the tank), dispersing heat throughout the tank.

Another area where heat loss is the highest (which explains why the back of the tank is cooler) are the openings at the back part of the canopy that allows for heaters, filters, airstone tubes, etc. versus the closed lid at the front.

The last thing to check is how big of a temperature difference are we looking at? To negatively affect the health of fish, there has to be a 8-9 degree F change (4-5C) and it has to be sudden. If you are looking at 2-3F difference from one end of the tank to the other, then no worries. The fish activity will be your best indicator, if they mull around the heater or in one spot and do not utilize the entire tank, then start checking everything out. Hope this helps!

Thanks for the update...it definitely sounds like you have a water circulation issue. Swap the heaters from your two tanks to make sure it's not the heater. If that doesn't fix it, then drop a piece of plant into the outflow and watch to see if it makes its way around the tank. You may have to readjust your decor. And the absolutely last thing is to look at the location of your tank, is the back of the tank losing heat through glass because it's against an outside wall of the house? feel the wall to see how cold it is... if there is anything else you can tell me that you think would help? Do you have accurate thermometers?

Answer 2

It would seem that with any amount of circulation the temperature should even out. Does your tank sit against an outside wall where it may be getting cooler from outside temperatures? If you live in a cooler climate, the wall may be colder than the interior of your house and the thermometers could be picking up on these temperatures.

Also, is your heater one with an adjustable temperature, or is it preset by the factory? If it's adjustable, and since you mention it's a cheapie, does the adjustment go by actual temperature, or to you turn the know to + or -? Although it may seem obvious, be sure the heater isn't turned all the way to "+".

Is there anything blocking water movent near the filter (plants, driftwood, decorations)? I try to position them near the filter intake or the return so I know there's water movement near them (as opposed to in a corner of the tank which may be more "dead".

Anyway, 150s are a bit of overkill - you should only need to use 5 watts per gallon for most tanks (so that would be a 50 and a 100) unless you're raising the temperature more than 10o above the room temperature.

Answer 3

Yes you can. You just have to be very careful with a heater at all times cuz it just might get over heated and fish will pass... :(

Answer 4

You might be better off with two 25-50w heaters ( at opposing ends ) in your 20 gallon tank. This way the heat will be more evenly distributed. This is actually common practice among experienced fish keepers.

Answer 5

I had the same problem so I bought this Tetra heater and it works wonders. It stays at a constant 78 degree temperature.
Here is the link: http://www.tetra-fish.com/sites/tetrafish/catalog/productdetail.aspx?id=1276&cid=3080

Answer 6

call a heater specialist

Answer 7

probably buy a visitherm stealth it has a thermostat so you can set it at whatever you want