RunningWater

I dont have a heater in my 10 gallon tank with my mollies. Im curious though, is a flucuation from morning to night 78 - 82 and sometimes 84 degrees too much? The only thing i can think of is the incandescent light giving off too much heat. Is this bad for my fishies? or is it possibly more natural because thats how they would be in the wild? Just curious, they seem to be fine with the changes -- Nat

Dino

84 is about as warm as you should keep mollies.
As water warms, it hold less oxygen.

While 84 should be ok for mollies, any higher than that can lead to problems.
You might want to consider lessening the amount of time you light is on, to cool down the tank.

While fish may see a change in temperature over a season, water of more than a few inches deep generally does not have a temperature change on a daily basis.

Aquarium-Enthusiat

Well, I agree, 84 F is a little bit high for mollies. Also, any temperature fluctuations are not healthy for your fish. Fish are far more prone to contract disease if they don't have stable water conditions.

Here's what you can do:

1) Yes; try to decrease the amount of incandescent light that your aquarium gets.

2) You can also get a small fluorescent lamp (they're not too expensive) to replace the incandescent bulb.

3) And, if you're feeling really outgoing, you can get a bigger fish tank! As this Aquarium Care article (see Part 2) explains, larger aquariums 'suffer less from temperature, pH, and other fluctuations.

Think about it this way: if you pour a cup of boiling hot water into a small bucket that contains water at room temperature, the water in the bucket will get hot. If, on the other hand, you pour that same cup of boiling hot water into a large bucket of room temperature water, the temp. of the water in the bucket will raise only slightly.

Well, your incandescent light is like that cup of hot water in the above example.

This simple demonstration goes to show that the larger the body of water is, the less susceptible it is to environmental change! Large tanks are more stable, basically.

Hope this helps