ya i think a large patch like above would do it. if it was impossible for you to replace with a new one this would be your best bet. If you can find away to just get a new tank...... i would do that!
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Depending on how old it is. You could see if there is any warranty behind it and maybe the seller can help you with reaching out to Red Sea. If not, you can get a replacement through them but spending money trying to fix it is probably not worth it. Good luck!
Sorry Man ,That's not good . Particularly a tank that big ,500+gls?