I seem to find that moss grows on most things if your water is good enough and you water it well. If the water is three inches below the moss, you may not get enough wicking from the gravel to sustain the moss only that way. I would expect to have to water the moss daily or so depending on humidity levels in the tank (at least until it establishes). You may try sphagnum and keep it "mowed".
Drew

Except for sphagnum, I've always thought it necessary to give moss a soil-type mixture. I do know that Patrick at Saurian Enterprises (dart frog shop) is a big fan of the gravel-only method, so you might want to shoot him an e-mail. The link to his info can be found in the kingsnake classifieds.

Most of the moss I use comes off of tree branches. I haven't really tried the stuff you find on bad draining soil, I always figure I'd kill it with the good drainage my orchids need!

Drew

Hi
have you thought of bark chips or long fibered shagnum??
I find various types of moss show up on their own with this material. it does break down but both have a biostatic effect and it's almost impossible to overwater.
I'm using broken bricks to grow Selaginellas.( I know not really a moss) lol
gary

I emailed Patrick at Saurian Enterprises (thanx cdfortin)and will wait for his response, if he doesnt respond I will go ahead and try with the info you guys supplied, I will add five inches of gravel and four inches of RO water( thanx drew or) that will be drawn out of the tank, filtered by a canister filter, then returned from the filter to the water falls and drip wall, thanx garyfla, but Im trying to stay away from any "soil type" substrate as that seems to be where my problems always start =) Ill keep you guys up to date on my progress.

Good call on the filter too, I hadn't thought of that but I should have! Have fun with your project! I am jealous of you, I want to set my 29 gallon tank up as a nice terrarium but am moving soon so pretty much everything is on hold. I hate holding patterns.

Drew

Patrick gave me an email back and stated that it is almost impossible to grow moss on gravel due mostly to the moist humid conditions of tropical tanks, but I will not give up! "I must....grow....moss!" (in the voice of Capt Kirk!) drew or, when you get yourself settled in set up your tank and send in some pics, I have some pics in the gallery, check em out, its a 29 gallon going on a "piggy back" ride! LOL!

{{gwi:1268724}}

I grew moss in mine. Or rather, it grew it self. I snagged a small patch of moss from the woods and put it on a rock. Maybe 6 months later, it was growing on a log a few feet away. The moss you put in will probably never really attach itself, but it will toss off some spores that will latch on and grow where they can. Mine grows on this constantly moist limb of cypress.

-DH

I removed all the plants from the bottom of the tank and removed all the fouled soil,I will be adding the gravel tommorrow,I decided to try and grow moss on med sized river rocks,If moss can grow on rocks out doors I dont see why,if given the same conditions,it shouldnt grow in my tank,I will gather the moss covered rocks myself and place them on top of the gravel,my ferns are still growing strong along with the "papa gayo" and the one brom.I found a beautiful 10" pot over flowing with babytears,I will add a nice bunch next to the water fall,I will be adding the venting system also, it will be built into the canopy and will circulate the air in the tank,I will have more or less a "sealed" system,the only time I will have to remove the canopy will be once a week,as I plan on removing my critters for good =( I will be strictly plants now as I believe that I am not yet ready to handle critters,I hope to work my way up to keeping PDFs but will do so ONLY when I know that I can provide that PERFECT little slice of the rain forest for them, might take a year....might take twenty, only time will tell! =)

The entire floor of my terrarium is covered in a layer of living moss. The substrate is straight coconut coir and the moss I used started to grow naturally in my Bulbophyllum orchid pots. I removed the moss from the orchids pots and planted little plugs of moss into the terrarium. You could always use sphagnum moss over a drainage layer as a substrate. The sphagnum will eventually grow if given enough light and if only pure water is used. If the sphagnum does not grow itself other mosses will begin to grow on it or you can add others that you find and see what you can get to grow.

Moss in nature is part of a cycle and does not show up until the conditions are suitable. I don't think you will have success growing moss on rocks alone without a lot of trouble.

When you say "straight coconut coir" I know you mean with no other soils added but, do you mean right on the glass bottom of the tank? or right on the pvc grid of a false bottom? on gravel? Please reply! =)

I have two inches of Hydrotron pellets below the coir substrate. There is no water feature or drain involved but I have never run into problems with excess water. The coir stays evenly moist so I very rarely add water to the substrate layer. You could use a false bottom as long as you lay down some fiberglass window screen to stop the substrate from falling into the water.

The tank is a 24.5" high x 18" deep hexagon. The 3 back walls are covered in cork bark and tree fern using the Great stuff foam method. I mist the epiphyte walls daily but I cannot grow any serious moisture loving plants as epiphytes without adding sphagnum moss to help trap more moisture. I have an epiphytic fern, Bulbopyllum and Pleurothallid orchids, and Tillandsias mounted on the walls.

I saw it mentioned that sphagnum needs lots of light, but I find most of it here in the Pacific Northwest in low light areas. Usually S. facing, with a hillside to the N. that reflects full light most of the day, but never direct sun. I think that purity of water is key for mosses. I have found that 1/4 strength evenly balanced fertilizers in rain water have little to no impact on the different variety of mosses. (I grow orchids, so I try to keep the moss happy but if it's moss or an orchid you know what wins. You should see what happens to the moss on my noble Dendrobiums when the winter dry spell comes on!)
Let me know if this is enough information for you,
Drew