i think its called weldon, you can buy it at a hobby shop. home depot carries silicone thats made to adhere to acrylic. if your just making baffles the silicone will work, i just did my baffles. i used super glue first to hold them in place, then siliconed.
Thanks also I wanna get a few acrylic peiecs just for some bracing .I just bought a large acrylic sump and 2 sides are slightly bowed about an 1/8 of an in on top so I figured maybe I can add some bracing on top to stop any deflection do u think this would work for