Questions - Need some input

I test for nitrates and phosphates test kits from redsea.
My nitrates show that they are at 0.00 and the phosphate test I am not getting no chemical reaction in the test. Hair algae is starting to grow more. Can something else be causing it. I have a new rodi unit and do a water change every 2 weeks about 20%. What else can I do?

Anyone have any wall hammer corals to give some advice on? We're should these corals be placed? Middle or low in the tank? In the sand or on rock? I am using 2 radions at about 50% power right now.

Red leaf lettuce, is this good to have growing in my tank? It Started growing out of the blue, no its the size of a softball. Do I keep it in tank or put in the refuge?

this is my first entry on reef addicts. I am looking for some advice and guidence. I have been in this hobby for about 8 years. I have let my tank go down hill when everything that I was bought would die. A few times i wanted to take down my 90 gallon but could not bring my self to it. Recently I found out that I have been giving wrong info from the LFS, I have installed a refugium with live sand, rubble rock, cheato, a bio pellet reactor and a reef octopus 6 skimmer. I still need to upgrade ...