Another thing to consider when testing for nitrate, or phosphate in our tanks is that the tests most of us use are rather limited in their abilities.
The presence of algae in a tank is a clear indicator that some levels of each are present even if the test kits show nothing at all. The algae is just uptaking the nutrients as fast as they become available in the water.
Thinnk of it like ammonia in our tanks. Beneficial bacteria become populous enough to consume all the amonia inour tanks, but the ammonia is still present. Dying microorganisms and fish waste produce it on a constant basis. A test of zero means you have hit an equilibrium between consuming factors (like algae or bacteria) and producing factors (like decaying material and fish waste).
You need to start controlling the introduction of nutrients into your tank and then start selectivly reducing the quantities of nutrients.
Use only RO-DI water (well water can have untestable compunds in it that will feed algae like iron). And try using a phosphate reactor and heavy protien skimming.
Controlled feeding is another good idea. I only feed about every two to three days. And I only use quality foods, (spectrum thera A+) and rinse my frozen food.
You might also want to check out your tanks parameters for alkalinity (dKH) and pH. Improper levels of either usually accompanies algae blooms and maintaining proper levels helps create an enviroment that is not favorable for algae. I keep my dKH at 11 dKH and my pH at 8.4.
Also be aware that phosphate media can use the alkalinity in a tank when it soaks up the phosphates from the water. So testing becomes even more important then. Manual dosing of 2 part solution or superbuffer dKH (soda ash) becomes important if you see your dKH levels drop.
Even at three months, your rockwork is still potentially in the middle of a cure process. Not all rock is created equal. I do a presentation for local reef clubs about making aragocrete (man made live rock). Part of the presentation is about what happens to the rock as it develops and becomes live. At the end of the presentation, I do a pretty interesting experiment where I compare the aragocrete to normal Fiji rock and some premium rock. Trust me, not all rock is the same! Here is a link to the presentation. Just skip to the end.
http://www.airinheresreef.com/Aragocrete Rock.html
I also have a short article about water. It is by no means comprehensive, but it does give some helpful insight.
http://www.airinheresreef.com/Water.html
