Ok guys i've thought of a new idea for a cave and just like to share it with you. (Unfortunately I have to use internet pictures as i can't get any pics off my camera to the comp atm (lost my data cable)).
Clean water bottle (no other types as there will be contaminants in them)
Sharp scissors/knife (Caution with blades as they have the right to slip and cut you at any given time)
1. Get a 600ml water bottle or whatever size you want your cave to be
2.Get the water bottle and 1.5 inches from the base, make 3 small holes near each other (air holes).
3.Next, cut the bottle in half so it looks like a cup. Then cut the cup shaped part of the bottle in half again so it looks like half a cup.
(the red lines are where the bottle should be cut so it looks like half a cylinder)
4. After you have the desired shape for your cave grap some silicone and smear it over the outer surface of the cave. Grab some substrate from your tank and adhere it to the bottle. Once it is dry, you may again smother the substrate in silicone to apply another layer, if the first layer isn't thick enough.
5. Allow 7 days for the silicone to cure before placing your makeshift cave in your tank
I made my cave for my zebra otos but i have yet to test it out.
Once I get my camera working again I will post proper pictures(sorry about this one I have, poorly displayed)