switching from plastic to live

How much light, and what diameter is the gravel(fine, coarse , pea-size)?
You can do it gradually if you have enough light and small enough dia. gravel to support plants.
Any other information you can give regarding filtration, test kits etc. would help us make suggestions.

Len

First of all, 1/4" of gravel is not going to be of much help when growing plants.
I use about 1.5" in the front, sloping up to 4 - 4.5" in the back for taller plants. My depth is more than most people use, I think.
I don't know why anyone would tell you to cut down to 1/4".
Can you give us a rough estimate of the size of the gravel in mms.? You might want to add back to your substrate with a more plant friendly material, since you've got much of it out anyway.
Your heat does not have to be that high for a planted tank. 76° or so would do fine.
An AC MINI is kind of small for a 20 gal. tank, but if you keep your fish load down it should be OK, if cleaned regularly.

There is another member starting out with plants, just as you are, named Blinky I think. Read his/her post and responses to it for more info. I left a link on my reply, for a really nice site that would probably help you and answer some of your questions as well.

Len

djlen said:

I don't know why anyone would tell you to cut down to 1/4".

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In a tank with no live plants, more than 1/4" is unneeded and will only make cleaning more difficult. It was probably good advice at the time but will need to change with the addition of live plants.

One easy way to start with live plants without changing your substrate is to buy some plants that attach to wood. Probably the easiest plant to grow is called Java Fern and it should be readily available at almost any LFS. You can attach it to some wood with a piece of string and it's roots will, with time, hang onto the wood. With 1.5 watts of light per gallon of water you should be able to grow quite a few nice plants like hornwort, some crypts, anubias, java fern & java moss. There are a lot of threads about low-light plants so do a search here in the Aquatic Plants forum.

If you find you like the live plants and want to get a bit more serious about the hobby you should consider re-doing the substrate which means draining the tank and basically setting it up all over again.

Let us know how it turns out.