Stop the iodine. Save it for bringing in new specimens or for cuttings.
change 10% of the water every 2 weeks.
Bring the temp up as already suggested.
How did you decide on once a week Calcium and Alkalinity supplementation?
Do you document the lack of growth with a weekly series of photographs of the tank? You may be surprised with how much growth you actually see by doing this.
Change the refugium bulb to a LOA outdoor reflector from Home Despot or other home improvement store, they are 6500 K fluorescent bulbs and 65 watts for about $35 USD and are easy to install*.
You didn't mention the
coral specimens in the tank, what else is in the tank besides the inverts, fish and corallimorphs? Many of the organisms you've mentioned don't just jump up and show visible weekly growths, especially in new tanks (believe me, 3 months of maturation for a tank is NOTHING.) Your system has had little time to develop much in terms of food chains that help stabilize carbon cycles in the tank that lead to good controlled growth. Just because your
nitrogen cycle products are producing nitrate does not mean that the carbon cycle's food chains have come anywhere close to maturation. In addition, denitrification has prolly not started to produce results of any significance at this point, so nitrate accumulation may also be impacting your system's productivity.
A posting of your husbandry schedules, your lab values and testing methodology for the water parameters, and a feeding schedule with realistic responses will tell us much more, but keep in mind as Mike has already posted, nothing good ever happens quickly in a reef tank.
I get excited when I have 1 cm a month axial growth in a 2 year old (relatively young) SPS tank. Now THAT'S rapid growth by closed system reef coral standards, and will be specie-dependent. It seems that Spanky has a semi-open system in the Keys with some fast growing Staghorn
Acroporids, but getting to that point in closed systems requires maturity, perfect water, and STABILITY for the parameters in such a system. About the only thing that happens quickly are the things like
Aiptasia blooms, nuisance algal blooms, cyanobacterial mat developments, or flatworm blooms. Most are linked to sudden vacuums in the food chain or gradual accumulation of some substance(s) that cross a trigger threshold. These may be due to either a lack of diversity and/or excess nutrient availability, or specimen loss due to water column instability. These events are often the harbinger of downward spirals that may lead to total system failure if not detected and corrected early in the sequela of events. This is not saying your lack of growth is due to the above, but rather to point out that
nothing good ever happens quickly in a reef system, only the bad stuff. Patience becomes the reefer's mantra when evaluating your system's progress.
Sorry to ramble on like this, a good evaluation of your system will probably show that there may be some immaturity issues, but that your system
seems to be on track at this point, and that some small tweaks now may improve your long-term outcomes with the system, but for the most part, your system is doing OK.
HTH
*
If you're good with electrical wiring, you'll need some 14/2 wire, a wall switch and outlet box, cover plate for the wall switch, some flexible conduit, a 3-pronged utility cord, and some wire nuts to finish this install, as well as a round utility electrical box for the actual reflector install on a suitable mounting device or hood. Assembly should be straightforward, if you're not totally comfortable with this, have a qualified electrician set this up for you.
