The intial surge (or lack thereof) of alage "outbreaks" may or may not happen for many, many reasons, from source of live rock (dry/dead/fresh/re-used), source of sand (dry/dead/fresh/re-used), if running lights during initial "waiting/cycling" period, any ammonia additive to "jump-start" tank (shrimp/fish/bottled bacteria), on and on and on. I've seen it go both ways countless times, and if you want to, you can surely prevent the outbreak, but by no means does it have to be one way or the other. Markus noted that the algae has subsided, which it generally will after a while if you see an "outbreak" during start up.
Eggcrate will leach some PO4 into the water column. You can prevent this by soaking the eggcrate in RO/DI water and doing 100% water changes every day to every few days until the RO/DI water reads 0 ppm PO4. You're "leaching" the PO4 out of the eggcrate prior to intoducing into the tank. Is it necessary? Not really, but it does ensure your not introducing any uunecessary PO4 into the water column, however the amount is generally negligible.
Tank looks great Markus :thumbsup: