Flatworms in the 40 reef... what do I get?

[Isosceles]

Brown flatworms... I know, not the best practice to get fish just to fix a problem, but I was considering all of these for the tank regardless. The tank is going to be without fish for awhile as I am running fallow for ich, but I figure I can throw the newcomer into quarantine with the current residents while the tank settles. I read about mandarins working too but that wouldn't work out too good if I'm going to be keeping everything in a bare quarantine for the next 2 months. I however, also read that maintaining specific parameters can also help mitigate or even eliminate the issue. What do you think?

Current livestock:

Ocellaris clowns (A. ocellaris) x 2
Pink skunk clown (A. perideraion) x 1
Bicolor blenny (E. bicolor) x 1
Banggai cardinal (P. kauderni) x 1

Legit peppermint shrimp (L. wurdemanni) x 1
Electric blue hermits (C. elegans) x 2
Orange claw hermits (C. tibicens) x 4
Scarlet hermits (P. cadenati) x 4
Blue leg hermits (C. tricolor) x ???
Halloween hermit (C. strigatus) x 1
Tiger conch (C. luhuanus) x 1
Astrea snails (A. tecta) x 3
Ninja star astrea snail (L. phoebium) x 1
Chestnut turbo snail (T. castanea) x 1
Giant nassarius snail (N. distortus) x 1

Planning to definitely get a watchman goby.

Current parameters:

Temp: 78.9F
pH: 8.0[!]
Alkalinity: 5.4[!] dKH
Magnesium: 1440 ppm
Nitrates: 1.5ppm
Phosphates unknown... I don't have a test kit at home

Perhaps it's time to start dosing...

 

[Uncle99]

I use Salifert exit for 2 hours then I pull it out with carbon twice with 7 days in between those two treatments.

To keep them in check, I use a couple wrasses.