Undergravel heater
 

I've read books in the past that suggest using a heater under your gravel, or under your tank if keeping plants.

Thoughts?

its supposed to help by providing a uniform heat in the substrate, this will also aid the uptake of nutrients.
I didnt do it. but if i were to strip my tank down i would.
It also means that you wont have to have an unsightly heater in your tank!
:)
a.

I don't know of anyone with heavily planted tanks using them in the US. If you don't want to see a heater, use an inline heater, which connects to the output tubes of your canister filter.

Eddie now you do.

We run a Duplamat 150 in our 20g. The theory being that it keeps the substrate warm. Warm air and water seem to rise. This creates a convection through the substrate. As the warm water leaves the cool water replaces it, thus flushing the roots with nutrients. Can't say for sure if it helps or not due to lack of trying it any other way. My LFS (which has several awesome plant tanks) swears by them. If you look under the stands you'll see giant root masses.

Cool.

They're are not just that popular from the many planted tank forums I belong to. As far as the benefits, I know many of them have BEAUTIFUL planted tanks using glass heaters or in-line heaters.

As far as getting nutrients for the plants, most of it is just achieved through the water column. A good current is all that's needed. If you notice when you pour liquid nutrients in the water, it sinks then spreads around the tank via the current. I guess you wouldn't want the nutrients to be pushed upward.

From the look of Andrews sig, he has a beautiful planted tank and not even using heating cables.

I asked a question on one of the planted tank forums I belong to regarding their use and here is one of the replies I received...

Imo they are not worth the money in a planted tank for the same reasons pointed out by eddie.

Thanks for your thoughts -- I havent' really seen any in the lfs, and wondered if there was any real advantage. There is definately a temp difference in the water above the gravel and below, but wasn't sure how much that affects the plants themselves.

Plants are not that sensitive to temp differences. I've tossed plants from my heated tanks 82°F (28°C) into a 5.5 gallon unheated tank (I would assume about 72°F) with only a filter and a desk lamp and they are still surviving. I dare not do that with any fish.

well of course it makes a difference, current or not you are not going to get uniform heat any other way, have you noticed the temperature of the water 3/4 down, and how the water is cool in the thick of plants???
Undergravel heat is a way of ensuring a balance heat for plants, a heater inline or in the tank wont provide the same temp balance for every tank. They can be used to great effect with carpet o=plants, there is nothing to suggest you can carpet without it, but you will see quicker more positive results with this method. As for the inline method, this is an expensive heater to run, and quite wasteful, quite green here in the uk, so will stick to intank heaters.

The only draw back i can think of undergravel heaters in the delay between heating the substrate and the temperature probe reading in the body of water, the delay might give rise to temp fluctuations until you have the settings down.