Loricariidae and housing requirements

[fishfever]

I set up a 20 gallon aquarium with #8 L046 zebra plecos between 1.5 & 2.5 inches in length.

No gravel;
15 Watt fluorescent light fixture on continuously;
outside power filter 200gph and 50-75% water change every 2 weeks or so - conductivity is about 300ms -ish.
heater at 81-ish degrees F
I feed daily - each day a different dry food of a sinking variety and once weekly frozen brine shrimp, daphnia, or grouper eggs etc. (I find it easy to monitor their food consumption by siphoning the poop and any residual food off the glass bottom with a piece of air line tubing every 1-2 days).
#3 reasonably thick 6 inch Anubias plants each rubber-banded to a pvc pipe (1.5" diameter & about 4" long open both ends)
Brick caves in two sizes - I siliconed two bricks side to side with the holes that go thru them together and sealed one end with a flat slate such that there are now brick tubes in two different diameters.

My question is in reference to the hight of the entrance to these "caves" off the aqaurium floor. I have noticed over the last few weeks that no 046ers have taken residence in caves that have entrances above the floor - simulating a small cliff with holes in the face. All tenants reside in the caves that have entrances that are flush with the aqarium floor.

any comments ...

[Shane]

Fishfever,
Zebras do not spawn in holes in the riverbank like Hypostomus, Glyptopterichthys, and other Hypostominae. They live in deep waters and spawn in cracks in rocks that they wedge themselves in. A raised cave would not be "natural" for them unless it was stuck between rocks to simulate a crack or crevice.
Light is also very weak that deep down. I am not sure why you would leave the lights on all the time. 8-10 hours a day would be plenty.
-Shane