[Dyesub Dave]

HMMMM .... I hadn't heard that before but it seems to make sense. The original site that I found just mentioned to use charcoal so I did. I haven't noticed any problems using it however I've read that it's an unnecessary step.

I have a couple of enclosures that don't use it but many of them do. It would certainly be a PITA to change it out every so often!

Dyesub Dave.

[Hilde]

If by chance you do decide to go ahead and have water sitting in the bottom, you might find the odour unbearable after a while. It will go stagnant unless it's being oxygenated. Even such a small volume can stink up a room after a while.
Even though I don't have standing water under the soil, I've placed old under-gravel-filter plates under my gravel layer, complete with upriser stem long enough to be an inch or two above the soil surface. The stem is in a front corner, easy to get at. If I notice there's any water build-up, I can insert some airline tubing to siphon out the excess water. Generally it's not a problem with careful watering, but once I did manage to dump some water accidentally and had to siphon it out after it filtered down.
In your case, which is basically an uncirculated pond, it's still a false bottom and anaerobic water ... not good for the nose and possibly can grow bacteria that might be hard on the geckos. It will certainly contirbute to mold growth. Having an access tube to siphon the water out once in a while might be worth considering.
I'd suggest you stick with the hydroton balls.

[Tdizzle10]

ive pretty much done what i said i was gonna do and theirs not that much water in their.. after an hour or so it evaporates so it relatively dry in the water part right now, and on top of the eggcrate holding my soil is like 4-5 inches of substrate