Amie wrote: One thing that I forget sometimes when adding phyto to my tank is that it will increase the salinity of the tank.  I think Mark adds phyto when he does a water change.

I remove the same amount of salt water BEFORE I put the phyto in.  Ie., when I put a gallon of phyto in, I first remove a gallon of water from the system!  That way it does not affect your salinity!

Mark Peterson wrote: Wow, Amie sure is fast at the keyboard!

You are not the first one to accuse me of that.

One thing that I forget sometimes when adding phyto to my tank is that it will increase the salinity of the tank.  I think Mark adds phyto when he does a water change. 

Just DON'T ask Mark how much phyto he adds to his tanks!  His huge clams definitely love him!

I add a gallon to my 75 gallon and a gallon to my daughter-in-law's 55 gallon tank every other day.  I have never had a problem with a phyto bloom.

As posted earlier, it really depends on what you have that will eat it!

 Tanks of all sizes are susceptible to a bloom of phyto, if the organisms eat it slower than it grows.

Wow, Amie sure is fast at the keyboard!

I believe in fertilizer as a means of encouraging the growth of phyto over other things that could grow in the vessel like bacteria and fungus. 

How much phyto a tank can handle really depends on how much life is in the tank.  If you have lots of clams, you can probably add as much as you want.  I have a 45 gallon with lots of softies & LPS, live rock, live sand, 5 fish, and a refugium with lots of life in it (no clams).  I add a quart of phyto twice a week and everything seems happy.   I also have 42 gallon fish only tank with live rock and sand, but I only add about a two cups a week to that tank.  There's just not enough life in that tank to eat the phyto and I don't want it to turn into a "phyto farm". (Been there, done that. )

Adam Haycock should pipe in to answer your questions about fertilizer.  I thought you had to have it, but I really don't know.