OK, by marin standards phosphate .05 is not a super low level, you preferably want to be testing zero. However as the majority of test kits, apart from the Merck one, are somewhat inaacurate you can really only use them as no,yes,lots tests.
Cleaning the algae by hand will be an increasingly hard battle. When full grown hair algae kicks in you'll find it can grow an inch a day. A lot of people will tell you, and I agree with them, that while dissolved ammonia, nitrate and p are important, the fun really starts when the stuff is just long enough to trap debris - that's why part of the algae war is to have pretty strong circ - when your turnover is 25x per hour you don't see much trapped debris.
When ammonia goes to zero get the cleanup crew in. Nitrite is less anissue as it's not toxic in that pH and with all the Cl- ions dissolved in the water.
Marine ich is similar to fresh in appearance, but in your setup will be a sod to fix. Certainly now we won't be able to copper the tank as 1. it iwll kill everything and 2. all the CaCO3 in your tank will absorb it as fast as you're putting it in. Thus IF you have ich you will probably want to hypo the tank, which means you reduce the salinity to about half of normal or a bit lower. This is a nice soft cure, and effective, unlike some other cures people will suggest (Kick Ich, RX-P and garlic are all ineffective i.m.o.) but first you have to make sure it is ich, and not just stirred up debris. It will look like little sugary crystals.
If you hypo the tank do not put the cleanup crew in as the reduced salinity will certainly kill snails though crabs are usually able to handle it down to a salinity of 1.010. But beware, cyano slime algae loves hypo so you will likely get a huge bloom of that, but you can easy fix that when you've finished. Also don't put the LR rubble in to reduced salinity water. You will be running hypo for a full month or 6 weeks, so if you have to get the rubble then put it in a yoghurt or ice cream pot a couple of gallons in size with some salt water and float it in the tank to keep it warm.
As I understand it you have three normal out put fluor tubes over a 90 deep. That is not going to keep you going with any photosynthetic organisms I can think of. I think you could try mushrooms, but that's it. You can keep photosynthetic orgs under fluorescents (I do it) but they don't punch far into the water, so anything deeper than a foot or so is too deep.