Janet makes an excellent observation.

Since you put so much Borax in your pool, it will be worth it to get Borate test strips (They measure the Borate level--which is what Borax adds). I will speculate that your borate level is fairly high, but probably not the ideal of 50ppm.

Still one of the beneficial side effects of a high borate level is its very strong algaecide property, which may be why you haven't had an algae bloom if, as Jan suspects, your CYA is higher than we normally recommend.

Carl