lol dang 2.5 huh, pictures dont really do stuff justice and i guess its true it looks bigger in camera hahaha...okok, imo thats going to be way to small because you will want to keep your return away from the chaeto area due to clogging and such so theres one baffle there easy, youll also want a buffer from your incoming water flow to slow the water through the refugium...so thats 2 baffles. I think that would be a bare min but wouldnt be what you want and would quickly see the value in baffles in refugium. In the pic I sent earlier in thread shows a 40 gal and I was able to manage 13 1/2 inches long by 16 inches wide for a refugium space. Now granted I used a 5 inch space for my return and those baffles leading up to it take up 4 inches total, 3 baffles spaced 2in, and I used a 7 inch space for my incoming water flow, filtration area and have a protein skimmer in it as well....I also just added another pump in there for the reactor so its feeding out of there too.....anyway the baffles leading away from the filtration area are 6 inches 3 baffles spaced 3 inches. I did this because I have bio balls in between them as a place for them to do there job and they look good there.
That is an example of what goes into the thought of making a refugium....I have been able to do this in something as little as a 10 gallon but..... I could only use 2 baffles per side and the incoming water was strong enough to still disturb the refugium side even through filter, on top of that the intake side was really crappy and it left my filter in the water at all times (which you wont have a issue with with your uniquarium), but defeated my filtration, my return side was fine....Those are some mistakes Ive made. Now with that all said in my honest opinion with the space you got you can make a 10 gallon aquarium with 3 baffles on the intake side to slow water flow and two on the return side so you can save space.......now your wondering why only this many baffles why cant I put as many as I want....well you can and the more you have the better....but when it comes to building your own and using 100% silicon to glue it up (or what ever you choose) you run into the issue of being able to fit your hand in between the baffles to give them a good seal...and anyone whos tried to make there own will tell you if you dont make them well the silicon will come off the glass and acrylic or lexan causing a failure in your refugium/sump.
I hope I have been some help or given you some incite on what to do and what to expect so you don't do like me and run into those issues when they happen. Also about the reactor suggestion, I just bought this one and I think you could put a little sand bed in the bottom of it with some chaeto and grow your pods and chaeto with out having all the extras, but I don't know for sure. Ive heard of people running a substrate bottom in them, and the phosguard I have in mine now doesn't tumble so any substrate bed would stay un turned and allow life, not to mention they should just hide in the tangle of chaeto and be happy there if im not mistaken.... But this is a theory of mine based on hearing what others do with there reactors and they way this specific one I have runs. heres the link if you wanna check it out, its a 5.5 inch Dia and its a good size, can do up to 200 gal but I believe a little more.
https://www.amazon.com/dp/B00GYG54ZU/ref=psdc_2975472011_t1_B00GYG54O6
