How to tell if my tank is tempered?

Well after thinking about it for several weeks not I have decided to make a closed loop system for the oceans motion 4 way and drill my tank. Question is how do I know id the bottom of my tank in tempered as I have heard you cant drill tempered glass. The plan is to make a internal return for my sump and then obviously a separate feed for the closed loop system for the OC 4 way. This will be the first time I have ever cut a hole in glass so obviously I will practice on some scrap and make sure I am steady.

I have been reading everything I can find and thinking of moving my tank anyway to a location where I need both front and back to be presentable this seems like a very good option. Also this would give me a chance to add another hard piped tube with separate valve strictly for water changes I would set at 15%.

Anyway is it true you can not drill tempered glass or does it just tank longer? If it is true then how do I know if my glass is tempered at the bottom? Its a 90 gallon Oceanic tank that is about 7-10 years old I think.

If the bottom happens to be tempered and I am forced to go through the back then I guess leaving it in its current location is my only option and then I will re-think the entire situation.

 

Sounds good & yes you can NOT drill tempered glass. It should say it, if not you can alway call the Mfg.

 

Another trick is to put on a pair of polarized sunglasses. Tempered glass will have a pattern to it that can be seen. But always a good idea to contact the mfg for confirmation.

 

I would guess it is tempered based on the size. Also think about making holes in the pane of glass that is bearing the most weight.