Nitrate/phosphate questions

Got a couple of questions... Trying to better understand how to control my cyano and brown algae problem. Iam getting there, but my phosphates are not going down as quick as I would like. I am using RODI water. My nitrates have been at zero for awhile now. Using the Hanna checker, my phosphate has gone from from 120 ppm to 73 and is now at 69. I am trying chemipure elite and have a good size cleaner pack coming tomorrow... Snails and crabs. Was thinking abot adding cheato, but:

1- will chaeto lower phosphates, or just nitrates?

2- if my tank is overstocked, will that cause, high phosphates, or just high nitrates.

3- is my tank overstocked? 54gal bow front. I have 2 yellowtail damsels, 2 clowns, 2 engineer gobies, a fire fish and a royal gramma.

Have only been using RODI water since December. I think my rock and substrate was just so absorbed with phosphates, it is just going slower than I had hoped getting back in order.

Many thanks. Only have been a member for a short time, but this forum is giving me much knowledge to better understand this hobby.

 

Btw, I am FOWLR at this point. No corals

 

1) phosphates too.

2) it shouldn't, but the food we feed has phosphates in it.

3)not for a fish only tank.