Looks like the tank isn’t leveled and this would be a direct result of that. I do see the small area of separation from the initial setup. I also see the water level/height is higher on the left side of the tank right on that seam. My guess is its leaning forward a bit there also placing more pressure than usual on the front left seam. Had a 300 just like this, same front corner also lol… was my first acrylic i set up and it was unlevel in the same way. I watched an exact area of separation form like this for 10yrs. I was also lazy and never fixed it. Sold the tank recently. I did lower my water level below the area of separation tho to relieve some of the pressure. It never spread into the seam after almost 12yrs.
Only thing u can do with the tank running, even half full is to drill into ur overflow box to lower the water level.
Do Not use any type of solvent glue on that seam while the tank is full or half full. It will make it worse. Solvent glue melts the acrylic a bit before it fuses and if that happens under pressure it will just push the panel further forward causing more separation.
How to move forward? … id get a 8’ intex pool with blow up ring or a stock type tank…repair the tank, re level it… then move everyone back. Only way sadly. Or u just cross ur fingers and let er run as is. IME acrylics really never “explode”… they give u signs like this to know theres a problem and u do have time to address it. If anything it would most likely still b a small leak if it does spread to the seam.
Ways to fix it… few ways there also… id start with solvent #3 or 4… needle applicator and see if u can inject it into that white area from the side of the seam. After that id add in a 1/2” acrylic rod on the inside seam with weld on #16 or #40… 40 is much stronger but its not ideal using it indoors with its toxic fumes. U can “tip and pour” a 1/2” fillet of 40 on the seam also but this being an 8x4 tank u may not have help to do that. U can work on the tank as is with the rod method.
1 last way to fix it… use a 1/4” thick x 1-2” wide x (height of tank) “strip” of acrylic on the outside of the tank covering seam/joint top to bottom. Gotta use #40 for this tho IMO to end up working the best. U can really just slap it on with a piece of tape once applying the glue with a brush or ur finger. Its a bit messy but it works. I have also done this on a full tank that was leaking lol… #40 is not a solvent glue like 4 or 16… so theres no risk of weaking the joint as the glue cures.
Which ever way u choose to go repair wise, plan it out, take ur time and dont rush it. Ill try and get u some pics of the “patches” i have currently running. Ive repaired much much worse over the yrs… u have time to make moves if u choose too. It may not even spread further but theres always that worry/chance. The tank is def. Not level and i do believe thats y that area spread.
