Acrylic sump question

[Toxic enigma]

So a few days ago the sump on my 29 gallon reef mysteriously got a big crack in the back wall. I had planned on building one out of acrylic down the road but now I need a new sump a bit sooner. So I was wondering if I could just use the thicker stuff sold at Home depot to build one about the size of a 10 gallon, or does it have to be cell cast?

     

[roll_the_dice]

Probably too late for you, but maybe it will help someone down the road.  For your purpose the main difference is how it machines.  If you are cutting it with a saw extruded has a tendency to melt and leave burrs....where cast cuts smoother.  The smoother the cut the easier to join/glue with Weldon #3.  If you have jagged cuts, it may leak unless you used Weldon 16 in conjunction with the 3....the weldon 16 would be used more like a silicone to fill any cracks or jagged places in the joint.

 

That is the simplified version.

[Toxic enigma]

So basically the weldon 3 would be used to form the joints, then I'm guessing allowed to cure overnight. Then weldon 16 would be used to form a bead along the inside of all the joints to form a seal. This sound about right? 

[roll_the_dice]

Weldon 3 is water thin...and will actually bond the acrylic.  Back when I used to work with acrylic daily, I could water test a sump within a few hours of bonding.  How I used to use weldon 3 (I made a proprietary blend) I used to use push pins to hold the wall up then lay the weldon 3 under it, then pull the pins so the acrylic lays on top of the flat sheet.  This will give you a clear joint with no bubbles.  Hard to explain...google weldon 3 gluing....should find a plethora of info.