I tried to drill my 2.5, i have drilled over 50 tanks so far with no breaks, but they have been all 10g+. The 5g and 2.5g uses the same size glass. I found it is possible to drill a 2.5 and 5, but what you need to do is drill almost all the way through, stopping just before you push through, then get out a dremel with diamon bit and finish the job, went through 3 tanks like that. One tank I just took the back glass out, drilled a piece of acylic, siliconed it all back together, and its now running as a nano reef with no leaks or bows, so it is possible to do that also.