I only use carbon when doing equipment maintenance... such as taking the skimmer down for cleaning, replacing my micron sock, or when i have done a water change and kncoked some detritus into the water....
I have a 4-5" DSB and 120lbs of LR in a 90g. I have a total system turnover of about 1300gph.
I run it passivly. I have a bafffle system in my sump that allows me to run it, and maintain it easily.
I also run a phosphate sponge continuously. I use the Two little fishies PhosBan.. it doesnt leach phosphates.
There are two types of phosphate to be concerned with. Organic and in-organic. In organic PO4 is released by detritus and carbon..( all of which was orgainc at one time) this you can test with a test kit.
the organic stuff is a little harder to test for. this is tied up in molecules in the organisms and fish that are living. Algaes use this from first before the other. (when the animal has died immediatly and is starting to decay)
Green hair algae is the big problem with this. It grows and dies fast. grows when it has food and then outgrows its food source. Some of it dies, then some decide to use alternate food such as fdetritus. It is hairy because it traps the detrritus and decaying matter and converts it to food. So not only does it photsynthisis (spelling) it uses what i call a crap generator
so if you can control the phosphate and nitrate in your tank you can control the nuisance algaes. Now remember that algae is a good sign it shows you have the basic building blocks of life avail in your tank. the idea is to get the complex stuff to grow to outcompete the simpler algaes.....
but if you get a problem with green hair.... siphon all of the crap from the algae then scrape it off. then control the PO4 and NO3
I think i had too much chemistry. i shouldnt be able to remember this stuff
hth