i agree with donavan for small tanks i would use a 2 part calcium / alkalinity. i would check your calcium. stop adding every thing else{small amounts of iodine} but test your water outside of basic test kits

iv been doin saltwater for 5 years, the first 3 years i had no coraline and got pissed. Well thats what i got the salt setup for, color. 2 years ago i started testing. i ran a 30 gal with normal sp 0.021, i put 10lb lr in and tested. About 5 weeks into it i had blue and purple dominating. i found out you need a heavy growth of green algea to grow coraline. i found out the best way to grow the green algea in salt(with out a bloom), is to add doses of freshwater plant ferilizer. just 1 dose the first week, and wait bout 4 weeks and add anouther. the purple and deep turquois will eat the green algea. once you see the coroline covering a few rocks stop adding the fert, the coroline will take over. make sure you watch the ph.

so far its worked for me. i do normal waterchanges, and check levels, truthfuly i haven't had any major problems. like i said, ph is the only thing realy effected, and it wasn't dramatic. the stuff i use is Plant Gro, im not trying to screw anyone over with bad advice. im just saying it worked for me.

absolutley, use the B-ionic calcium and alkalinity components along with purple up, the purple up is just concentrated calcium, it must already be living on rocks or glass, without good water quality it wont work. also buy new live rock that is covered in coralline and i gurantee it works. upgrade your lights also, shoot for atleast 5 watts per gallon. i started growing coralline two weeks into cycling my tank using b-ionic, but no matter what it will take time to spread, remember...only bad things happen fast in this hobby