My dad hasnt ran the upgound jacuzi in years and when i opened it to ther the water was still in it along with this red/brown looking stuff, im assuming its algea. i drained the spa and sanitized it before we filled it up, heck we got it looking brand new. we got all the new chemicals and now about 3-4 days after filling and all the levels being perfect the algea like stuff returned. anybody know what the heck this is? why its coming back/ how to get rid of it? i have no clue.
Thanks!

Welcome to TFP!

How did you disinfect? Did you superchlorinate to 100 ppm? If not, this post describes the proper procedure.