how long should i light for?

[wozza]

hi i have allways been unsure of this but never asked untill now.

so i have a 150w 10k MH pendent 10" above my water line, and my lights come on at 8am and go off at 8pm is this to long?

in my tank i have:
1 BTA
1 dersa clam
star polyps

cheers james

[Ninong]

Twelve hours is considered normal.

[wozza]

thanks ninong thats what i thought, just wasnt 100%.

cheers, james

[Reefland]

That is what we run our lights for. We only use metal halides and run them between 11-12 hours per day.

[wozza]

ok another question i think is related.

i think i can answer this myself but i would just like some clarifation on this.
my tank has been up for about 2-3 weeks with all that is in my signature.

i tested my water today and had these results:
Alk: 7.4 DKH (a little to low?)
Ca: 380ppm (a little to low?)
pH:8.2-8.3
NO3: 0ppm
PO4: 0ppm

but im still getting some algie growth on the glass and brown stuff and the sand bed, now im quite sure im gonna get told thats becuse its a new tank and thats cool with me.
But i was just wandering how am i getting growth if i have 0 neautrants (sp)
to feed it?
i have been testing since the tank was set up and its allways been 0 so i know the algie is not giving me a false reading.
oh and i run a fluidised reactor with 3x recomended of phosguard and carbon

confused james.

[Ninong]

The "brown stuff" is diatoms and it's a perfectly normal part of the initial cycle. It should disappear withing 10 days to two weeks on its own.

Both your alkalinity and your calcium are acceptable but a little on the low side. Ideally your calcium should be at least 425 ppm and your alkalinity at least 8 dKH. I like 425-475 ppm for calcium and 10-12 dKH for alk.

If your tank is only a few weeks old, it is not likely that you have zero NO3 and zero PO4. It is much more likely that your test kits are not very accurate.