Hi Fishfood !
Regular glass bottom tanks can be drilled as you know. When manufactured, regular flat sheet glass most often is cooled very quickly which results in a weaker piece of glass. Tempered glass on the other hand when it's made, is cooled very slowly. They temper flat glass here in town at several large glass plants that I've visited. They run it through annealing ovens that allow the glass to cool at a slower rate. It's just a lot stronger this way, can take a lot more force to break it, but it's most difficult to drill.
Without seeing the label ( like on an AllGlass tank bottom ) I don't know how one would tell if the glass is tempered. I can call an engineer I know at the glass plant and ask him on Monday if you want. Other than that .... maybe someone else here will know for sure. There may be a difference in color, or how the light passes through it, but I'm not 100% sure.
If you know the maker of the tank, you could call them or go visit a lfs that handles the product, and see if you can find out for sure.
There may be some tell tale signs to distinguish between the two different glass bottoms. Maybe.
As far as your sump/refugium plans - coming up with a design that works best for you, I'd be glad to help anyway I can.
If you've already thought about what I'm about to detail, please just disregard. But here's a couple things you may want to consider and give some additional thought to:
Use as big a container/tank as you can - especially if you're going to split it into half sump / half refugium.
As I'm sure you know, the refugium needs to be fed water from some place in the system. There are several ways to do this.
Some folks feed the refugium from the drain of the display tank. This may require a smaller individual drain line, teeing off a main drain line, and at least a ball valve in the line to be able to restrict some of the flow to the refugium. Personally I don't like any restrictions in my drains, but many go this route and it works fine for them.
Other folks have a separate gravity line that flows BACK to the main tank. This requires the refugium to be higher than the main tank in most every case.
Others, including myself, place everything under the tank and feed the refugium from the return pump. I went this way for couple reasons. I use external overflows - and did not want to reduce any flow from my main tank to the sump. It also was just easier for me to figure it out this way, and with using (2) 1" bulkheads and pipes from my refugium to allow water to flow back to the sump - seemed like a fairly foolproof way to prevent a flood.
In your case - you'll be able to partition "one" container/tank for both sump and refugium - which is a big plus. I could not do this and still keep the volumes of the containers as large as I wanted.
But it sounds like you can - and that's great !
You could tee off of your return pump with a small tee and tubing from hardware store. Run a branched line with small ball valve over to the refugium side to feed it water. Other end of the tee run's up to the main tank. Naturally as I'm sure you see, doing this will reduce the water flow to the main tank somewhat - and that amount all depends on the additional loss of head pressure from extra fittings and stuff, and how much water you choose to redirect over to the refugium.
Your "partition" or divider wall can be fairly high up in the sump box, with either slits or a V-notched weir, that will allow the raised water in the refugium to spill back over into your sump side. Ideal in my mind, as long as you can still regulate the flow with that ball valve.
Having the wall pretty high in the sump will allow you greater water volume and area to grow caulerpa, and give you more sump depth as well. Plus you have only ONE box of water under your tank - better in my mind for potential leaks.
The spray bar I used was for my main tank return. If I understand your question - you sound like you're considering this for your refugium as well. That would work fine.
In my case - I have (2) separate containers. If I just ran a hose from the tee off the return pump over to the "bottom" of the refugium side - when I shut off the return pump, or at power loss, the water in the refugium would siphon back over to the sump side. My 18 gallon refugium actually holds near 16 gallons, my sump is a 15 gallon container. You can see my delima. I HAD to feed the water to the refugium side from the "TOP". Upon loss of power - there is no chance of siphon - cause the feed line is at the surface and breaks siphon almost immediately.
In your case - one box with divider(s) - you should not have to worry about this as much - as long as you insure that your normal water levels in your sump is that which will allow the water draining back down from the main display tank to not overflow the sump.
The refugium will drain down to level of the slits or notch in the wall. This is if you feed your refugium from the top as well.
Just think of each compartment as it's own individual tank. How each compartment will be affected by the incoming and exiting flow of water, and how each compartment will interact with the other's water flows, ESPECIALLY upon loss of electric power. This is the kicker !
Lot's of other ways to accomplish what you want to do as well .... this just being one way.
I hope this helps you out some - sorry for lengthy reply, but feel free to keep this thread going if you want to, and let us know what you decide upon
