What are these red/pink/maroon-ish worms floating in my whirlpool tub? There's always a spa tab or two in the tub and it's kept covered when not in use.

We used it last weekend and it rained Monday onwards. There’s been a tablet always in the tub and it’s been covered though rain water does get in side as it’s just cover from leaves etc. Please help. Are these worms dangerous?