Originally Posted by Gomer4378
Everything has been perfect for 1 1/2 mo. and within this last week the diatoms went crazy....
No real answer for ya, but just a comment regarding the above quote...
When you first start up a tank, it takes months for a tank's parameters to even out. In reality, until you stop adding livestock, you tank is continually trying stabilize. Think of it as a really out-of-whack cruise control on a car that is going up and down hills - it really can never establish a stable speed. That's a lot like our tanks.
So the first thing to help solve the algae issue is to not assume that everything has been "perfect" for the first 45 days since cycling. In reality, your tank was just trying to figure things out. Algae (or cyanobacteria, as some of that appears to be) doesn't happen overnight. So don't knock yourself out trying to figure out "what changed" to make this happen... most likely it was happening all along but just took a month or two to become apparent.
When fighting algae issues, nitrate/phosphate readings will often read zero because the algae is consuming those nutrients as soon as they're produced. But they're there, or you wouldn't have algae issues. The fact that it sounds like your skimmer is producing quite a bit of skimmate kind of points to excess nutrients, since I wouldn't expect much from just two fish in a 150g system.
Are you feeding the coral anything? If so, what... and what are the corals?