Help Please!

[Unnerving]

I have had my tank running for 4 months now. No lost fish or invertabrates which is awesome because this is my first saltwater setup. About a month ago i noticed brown algae growing on the live rock which soon after turned green. I hear this is to be expected with a fairly new tank setup. Lately I have been getting a reddish-brown powder looking bacteria that is growing on the sand. Up until two weeks ago i was doing weekly 15% water changes and was about to do one today but all my perimeters are holding steady.
no3=10ppm
po2=.03
alk=7.2
ca=400
I don't dose anything since i haven't found it necessary yet. The only thing that changes after a water change is the calcium, it goes up to 450.
This is a FOWLR tank with 2 three striped damsels and a dogface puffer which is probably why my nitrates never drop below 10ppm.


Questions
1. Is the brown stuff growing on the sand normal for a newer tank?
2. Should i stick to the weekly water changes or can i cut them down a bit?

I have included some pictures to show what i am seeing.

 

[Dan06]

If you say it's brown looking, it's diatoms. It's typical of a new tank syndrome, most people get it within the first few weeks, and other won't get it for a few months. You can usually expect to have a bout with hair algae and cyano at some point down the road.

My algae blooms went like this:

Diatoms for about 3 weeks
Hair Algae for a few weeks
Cyano for about a month

Your phosphates are low, but that's likely because the diatoms are eating them up. I would actually slow down the water changes, be a little less generous on your feedings and give your tank some time to battle it out with the diatoms. Some people freak out at the sight of them and do massive water changes, or black out the tank for a few days. It's unsightly, but it's just some new tank syndrome. Ride'er out!

 

[Reefscape]

Yup...diatoms...just play the wating game with it...it will pass....

 

[Unnerving]

That's what i figured. So should i do biweekly or monthly water changes? Thank you for your help. Another thing, I'm running my light about 12 hrs a day. Actinics on at 10:30am, feed at 10:45am, 10,000k on at 11am, feed at 10:30pm, 10,000k off at 10:45pm, actinics off at 11pm. This was the best lighting schedule i could think of for my work schedule. I get off at 8pm, so would turning them on at 6pm and off at 2am be a better schedule. What about feeding times, i heard it should be during light hours, maybe 8:30pm and again at 1am?

 

[Dan06]

I've never experimented with the photo periods and feeding times. My lights are on from 4pm to 12pm and everything is thriving. I lightly feed every day.

I can't judge how long you should wait between water changes, but try to keep your Nitrates below 20 and if your phosphates start creeping up while you still have the diatoms, a water change won't hurt.

What size is your tank?

 

[Reefscape]

10% water change per week is acceptable..

 

[greech]

Turned my lights off for 3 days and they were gone. However, as soon as I kicked my light cycle back on they came back. Not much you can do but wait I'm afraid. Its just part of the process.