Hey - would this work and be simpler???
Keep the grate or whatever with rocks on top and crap falling underneath it.
Then, could you just use a regular canister filter and set it up so the intake is under the grate? Like have the intake tube go to the bottom of the tank and then go in an "L" shape so the intake hole is under the grate.
That way there's no drilling, no problem with power outage problems, etc.
You'd just have to clean the filter pads in the canister filter often.
thats very close to how my white's tree frog tank is filtered. I used half inch PVC pipe for a raised base about two inches up from the bottom of a 30 gallon high tank (20high on steroids) then i placed a piece of egg crate light diffuser over it cut to size with an opening for the water intake for the fluval 204 and a cord for a heater.
On top of the egg crate i used plastic canvas to keep the gravel from falling through under the plate. I only have about three to four gallons of water in the tank and the water return comes in through a water fall. I keep peace lillies in there to attend to some of the waste management but over all its been a great tank.
Two things i'd change, i'd use a heater with a remote adjustment next time (goin to after a move shortly) and i'm going to put back my optional under gravel return. I used a spray bar that i made for a fish tank and set it up so the riser was in the corner. Every time i noticed a sizeable amount of waste had settled under the gravel layer (its hard to tell the plant roots are taking up a lot of space). I'd move the water return line to the spray bar and let it run for a night or two and that would shove all the waste into the canister filter for a nice easy cleaning. With out doing that i'd literally go months between filter cleanings since the plants keep the nitrate low and so far i've never found anything else in the water.
About every four months i remove the frogs and newts and flood the tank so i can use the hydrovac to remove chunky waste like plant stems, small pieces of the driftwood, ect. Very rarely does it show up much but i do it anyway.
I'm going to make the modifications in about five weeks when we switch apartments and i'll try to get some pics and do a write up for it. I think this time instead of the plastic canvas i'll use Oddball's bonded pad idea. I"m just worried those blasted lillies will grow so tight into it i'll never get them back out. I had to eventually split the big clump since it was about to raise the roof on the tank.
I've been taking bits and pieces of ideas i've found to try and make the lowest maintence frog tank for the whites that i can.
Most my design came from reading an article years ago about a cabela's store and how they filtered their display tank using a raised grid holding large flat river rock about four to six inches in diameter and about an inch thick (the rocks that is) those allow almost all the waste to go through in a timely manner and get to the filter system for removal. I'm going to try this on another tank design i'm pondering (it may have to wait since i probably wont get a first floor apartment this time and i dont want to drop in on the neighbors when a 240 tests the floor).
What i'd like to find is a medium similar to gravel in its size that actually offers something to the plants but doesnt cloud up like the clay based aquatic plant gravel. I have to be careful though since i dont want to put anything in there that will nuke the frogs either.
Out of all this frog tanks i've made this is the one so far that i'm most proud of. If my 80 gallon tall wasnt looking its age i'd do a larger version and push the gravel bed up even higher and put some blind cave tetras under the plate in an artificial looking cave to keep the waste stirred up and add some action under there.
Well i've rambled enough time to go do some more research into those automated water changing ideas.
Take care everyone and i'll try to get a step by step write up done for the frog tank and if i get a chance to test it in my 100 gallon i'll do the same thing. Just not sure what the large gravel will do to my moronic AUL....i've had it on sand the entire time and i've seen that dense fish nose dive more than once....if i cause her any harm i'll never forgive myself.
Be well be safe and be happy.
Jason
PS i'd use an ehiem filter but that would cost more than my whole damn set up...as it was the filter/tank/heater/lighting came to about 220 bucks for a 20 dollar retail frog, how ever now i have two newts, and a green frog in there as well. Btw the heater hasnt been plugged in in over nine months i'm trying to keep the heat down for the newts...still holds damn near around 75 plus...i'm not happy i need to vent the lights better.