Gone for a month, need help fixing tank!

[Alex.M.]

I was gone from my 40 gallon salt water tank for roughly a month due to personal reasons. It was kept at my parents house however they didn't do much besides add one cube of frozen food a day. All my animals are alive and acting well however (now that I am back), I've noticed a lot more different colored and shaped algae all over the sand and mangrove roots. Can someone please help me ID this algae and what happened and how to correct everything. My tank is under-stocked. It only has one fire fish, one small clown, 2 B.cardinals, 1 urchin, 1 feather duster worm and like 100 mixed snails. My local fish store told me it was under-stocked so that is what I am going with.

The pictures aren't the best, I tried to include as much as possible, but without submerging my phone I wasn't able to get better pictures.

 

[lmforbis]

It doesn’t look too bad for a neglected tank, I was expecting much worse. A little hair algae is all I see. The fact that your urchin is doing fine says things aren’t too bad.
I’d do a couple 20% water changes over the next couple weeks and see what happens.

 

[beaslbob]

looks like you have some good things there. Like a possible turtle grass.

 

[beth]

The red is cyanobacteria and can become a plague in a tank if you don't deal with it.

Make sure that you have good water flow throughout the tank so that water is moving everywhere, every corner. Best conditions is when you your source water is at or near a zero using a TDS meter. Water quality is key so in-tank high water quality needs to be a priority. Also, while you are dealing with this, use overhead tank lights as little as possible.