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I've just bought a second tank second hand that used to have turtles in it.

But I'm a little concerned about the base of it.

It has a plastic base that holds the tank about a centimetre off the ground.

However there is no support under the bottom peice of glass, only around the outer edge.

Would this tank have had a peice of polystyrene to fill up the gap and support the glass?

Or is it fine being only supported around the outer edge?

Just seems strange to me to have a gap and only being supported around the outer edge.

What do you guys think?

How many liters is the tank?

Yup, some dimensions and glass thickness would help.

I've got a couple of 2 foot tanks on a plastic trim with a floating base and they have been great tanks for 30 plus years. I would assume there's a maximum size where this design would be advisable though. Test fill it outside and leave it full for a while if you have any doubts!

It looks to me like a tank that was designed for turtles, which means it is not meant to be filled with water to the top. The vertical glass panes are quite thin and not supported by braces. I wouldn't fill it more than halfway. Could make a nice paludarium...

OOPS- I did not look at the pics when I posted. What is below if for aquariums for fish , not the tank you have.

I have almost 30 tanks, at this point at least a dozen are empty. Every one of them has the same frame etc. you described. My smallest tank is a 5.5 gal. my two biggest are a 150 and a 125 gal. both were purchased used. They are actually perfectly safe to put on stands which only support the frame. I love this arrangement for some of my tanks with plecos. When they are on a frame type stand and I keep them bare bottom, I can look up from below and see a part of the pleco world we are usually denied.

That said, over the years I have had several tanks develop leaks. A 20L and a 75 leaked from the bottom of the tank. My original 45 leaked from close to the top.

That 150 I got used was ancient. It has very thick glass and a raised decal plaque from AllGlass in the lower left of the lengthwise panel. The silicone is holding fine but the part that extends out onto the glass beyond the joint has been peeling off.

So, I would assume the maker of your tank was reputable and followed proper construction metrics etc. So, you should not need to add anything under the bottom glass. In fact, I would think if you added a styro which did not compact enough and the entire bottom frame doesn't remain the primary point of support, it would likely break the tank.

As far as I can tell, the vertical panels are the max. height and the bottom sits inside these walls. This way the glass bottom is on the frame around its edges and all the walls of the tank are as well. If you think about it, the maximum PSI downward comes mostly from all the combined sides rather than the bottom glass in terms of the actual support. Then any lids etc.which rest atop the top frame will have their weight directed onto the bottom frame via the sides.

And then bigger tanks also have added support if they have more than one lid. Both frames have a matching horizontal which supports a lid while helping to minimize the glass bowing a bit and they also a support the bottom glass some (I think).

If the sides sat on top of the bottom glass, which would then occupy the entire bottom frame, the weight from the sides and what is on top of the tank would likely crack that glass. The frame must be the stronger point of support in terms of being able to handle the weight of everything by design. And that implies it is the way it should be, Otherwise I would have a lot of shatter glass and flooded rooms.