buy a large plexi top

Were can we get a plexi top for a tank
72 x 18 x 24

You can buy Plexiglas (acrylic) sheets at the home improvement stores and sometimes at hardware stores. Of course, it will need cutting to size, and the stuff is somewhat brittle. In addition, it will warp quite a bit. Some on-line plastic shops have larger and thicker pieces, but it will still warp.

A good alternative is a ready made glass hood. They're not expensive, and they're available from most of the on-line aquarium supply houses. You may need to buy two for a large aquarium. If you need a list of websites, just ask. You may need to check several suppliers. The suppliers usually list dimensions, and depth is adjustable by an inch or so. They even make flush mounted light/hood combinations for large aquariums.

My tank has no inside edge to rest the top on. That's way I'm unable to use the ones that are for sale now.

I have an acrylic tank without an inside recess, and the flush mount hood just sits on top of the thing. It has a glass pane under the lights and a hinged plastic panel. I bought it either from drsfostersmith.com or thatfishplace.com. In any case a glass hood or hoods would just lay flat on the aquarium top. Most large aquariums have top braces, so nothing is going to fall through.

It has no cross braces.It is 72x18 id
thank you
Dan

I had your same problem with my eighty gallon. It never had a middle brace. I could not afford a whole piece top so I went to home depot and bought some acrylic. I used some weld-on solvent cement and cemented a nice wide strip of acrylic across the top middle of my tank to serve as a resting point for the two hoods I did have. So far it has worked very well.

Welcome to the forum!

Weld On is the Stuff!