Adding insufficient chlorine repeatedly tends to be useless against established algae . . . even when you use more in total than would have been needed in one dose to kill the algae.

We need dimensions, an accurate volume, and a trustworthy CYA reading.

However, if you're in a hurry, and not too concerned about a lightened (or bleached) liner, in the EVENING add 10 gallons of PLAIN 8% bleach in a SINGLE dose. Follow that on succeeding days with 6 gallon doses each evening UNLESS your OTO shows an ORANGE chlorine test result.