Maintaining Heat

What's up everyone?

My 20 gallon tank's temperature keeps on fluctuating. Obviously, it's not keeping heat very well. How can I help insulate my tank so I can maintain a steady temp?

Thanks.

Before i can answer your questions let me ask some.

Is the tank located near a window?

Is it located where an AC vent could blow toward the tank?

And what kind of heating set up do you have?

Also, what type of cover are you using?

I have the same questions as above but my bp is in a 20gal long and I had the same problem. My screen is covered in duct tape and i have a human heat pad on warm side and a over head 75 watt red bulb on cool side which i use to have both on dimmers. My tank gets heat by the heat vent and the a/c vent and I was always adjusting temps which worried me when I would go away for the day or even at night when asleep.
So I invested in a ESU electronic temp control ( 27.00) ie a T-stat which works pretty good. I have it hooked up to the light and then I went all out and got a Helix control ( 120.00) for the warm side and now my temps stay at between 80-82 cool and 90-93 warm and I dont have to worry and it maintains good heat.
Get a t-stat you dont need to spend the $$ like I did on the Helix ( the Helix is for when my AP cage finally comes in with belly heat routed in ) the ESU works good.

With the seasonal shift (dramatic here) in temps you may need to relocate your setup to a place thats more stable. If you have one of the handy-dandy digi temp.hygro combos try using it to check the min/max temp fluctuation outside the tank (but in the same area). Those units can track the high and low temps so you'll have an idea what you are looking at in about a day. In a sense you have a box (cage) inside a box (the room its in) so there will be a fluctuation AND thermal lag, factor in a difference based on what size enclosure you have too.. Depends on how cool it gets at night and what time of the day your temps peak. Especially if you have window-unit a/c the temps can bounce wildly. We've ditched a lot of our heat-lamps recently since things warmed up so FAST - and last weekend popped in the window unit a/c - and the temps are dancing like mad so we're going to have to move a few.