To him it’s an acrylic enclosure. Another job among thousands of jobs. You build the box to the specifications that are requested. You tell the customer that it’s not safe to do so yet they request it be done that way regardless. Classic story. Look how many threads ask the question “can I use _ thickness material for X size build. The manufacturer recommends _”.
You can say no to doing the work, I completely agree. He does not have an engineering degree nor can he calculate fluid dynamics of your system. In the end it comes down to experience and what he deems safe. There is no guidelines for acrylic work out there. It’s an extremely tough topic to research. The pros don’t release their secrets as they shouldn’t.
In my opinion the customer needs to take some responsibility for their work request. You can recommend adding braces or reinforcing the seams with rods but in the end it’s their build.
I am not saying that is the case here but I can tell you that has been the case in multiple stories I have heard. Anyways, sorry this happened to you
@Josh. It really sucks to hear these kinds of stories. From someone who has had custom tanks fail on both ends of the spectrum as buyer and seller, I know the feeling. Hope it all works out for you buddy.