humidity with led
 

So I'm going to be getting the 29g diy from mod led so no fan needed. Will humidity be a problem 6 inchs above the water with no hood? What if I add a hood? On a different subject if I add a red and green module should I put them on blue dimmer or white?

You should put a small fan on the heatsink to keep it completely cool for the sake of your LED's. Humidity should not be a problem just make sure you have a splash gaurs to protect the LED's from water splash.

Any idea for doing that?

Ideas for the cooling fan attachment?

Well you could use some heat resistant silicone or some loc-tite super glue jel to attach it to the heatsink or drill & tap some holes in the heatsink.

No sorry, splash protection.

A simply clear acrylic piece heat formed to wrap up the 2 solid side of the heatsink attached with a couple stainless steel screws would do the trick.