Where do I start??? My new to me 18x18x24 ZooMed

[UncleChester]

Here is a question I have...Instead of buying eggcrate could one use larger (smooth river) rocks as the drainage layer then cover with the screening to keep the coco fiber out of the water?

Sure. This would be like the leca/hydroballs/hydroton approach but with rocks (the rocks will be heavier). I'm a fan of landscape fabric ('weed barrier') instead of window screening to keep the substrate from the drainage layer as it's nicer to work into funny shapes if needed, but screening works as well.

Make sure to test your new acquisition holds water before construction.

Great price by the way, nice find.

[J Teezy]

here's the thing with using large rocks. How heavy is that going to be? Just from prior hobby of keeping fish, the less weight you can put on the bottom glass the better. Since you will be covering the rocks up with a barrier and substrate, you might as well use hydroton if you dont want to use eggcrate. I would really not recommend using large rocks, Keep the weight down where possible! Hydroton is pretty cheap especially if you buy it at hyrdoponic store or garden store. Its the same stuff pet stores sell but doesn't have the typical pet store price hike on it