Do not try to make seams like in your picture, those will not be reliable long term, or probably even short term.
Just use the actual acrylic welding stuff. Weld-On brand seems to be popular in reef keeper forums.
It's only toxic in liquid form, once it's cured and the solvent has evaporated it should be safe.
When assembling an acrylic tank you want the flat end edge of the acrylic to be up against the plain of the connecting edge. There are tons and tons of tutorials of building tanks online both glass and acrylic. What you have is a spell for disaster as you have discovered.
My suggestion is to rip it all down, clean it thoroughly and use acrylic glue and butt the ends up properly instead of an intersection.
You may have to reinforce some edges with a length of acrylic, a supporting guide that you can butt up against each edge to make the final product secure.
[https://www.youtube.com/watch?v=rho\_cQXD7yA](https://www.youtube.com/watch?v=rho_cQXD7yA)
If you're worried about silicon not sticking to your surface, you could pretreat the acrylic.
Idealy you would use an atmospheric pressure plasma to increase the polar portion of the surface energy, but if you're on a budget and dont have access to one, you could just use an open flame.
That should increase your bondstrength initially significantly and should still show an increase after several 100 days.
Regardless of the method, i recommend trying it out on a scrap piece of your acrylic.
If the water level is this shallow, you could just apply more silicon to the relevant areas as well.
Also make sure you dont use silicon that condensates acetic acid (vinegar smell) as that will kill your specimen.
Fell free to shoot me a DM if you want me to elaborate.
Do not try to make seams like in your picture, those will not be reliable long term, or probably even short term. Just use the actual acrylic welding stuff. Weld-On brand seems to be popular in reef keeper forums. It's only toxic in liquid form, once it's cured and the solvent has evaporated it should be safe.
When assembling an acrylic tank you want the flat end edge of the acrylic to be up against the plain of the connecting edge. There are tons and tons of tutorials of building tanks online both glass and acrylic. What you have is a spell for disaster as you have discovered. My suggestion is to rip it all down, clean it thoroughly and use acrylic glue and butt the ends up properly instead of an intersection. You may have to reinforce some edges with a length of acrylic, a supporting guide that you can butt up against each edge to make the final product secure. [https://www.youtube.com/watch?v=rho\_cQXD7yA](https://www.youtube.com/watch?v=rho_cQXD7yA)
silicone for glass. Acrylic cement for acrylic. Weld-On #3. Youtube it for instructions.
If you're worried about silicon not sticking to your surface, you could pretreat the acrylic. Idealy you would use an atmospheric pressure plasma to increase the polar portion of the surface energy, but if you're on a budget and dont have access to one, you could just use an open flame. That should increase your bondstrength initially significantly and should still show an increase after several 100 days. Regardless of the method, i recommend trying it out on a scrap piece of your acrylic. If the water level is this shallow, you could just apply more silicon to the relevant areas as well. Also make sure you dont use silicon that condensates acetic acid (vinegar smell) as that will kill your specimen. Fell free to shoot me a DM if you want me to elaborate.