Coralline algae growing better under low light?

[Carissa]

I've had a fowlr 33g tank set up for about three and a half years and I've had extremely slow growth of coralline algae. After my lawnmower blenny died (transferring accident when I was moving the tank), I had this awful green hair algae that he must have been controlling, that went everywhere including on all my live rock. That was about two years ago now. I tried everything but finally hit upon the only solution that worked, which was to raise my lighting about 8" from the tank. So that stopped that problem and I've just been waiting for it to die off and pull it out etc. as needed. Nitrates and phosphate have always tested at or very near 0.

Anyway like I mentioned coralline algae was nearly non-existent or at best very slow growing. Even for about the 8 months I have been nearly free of the hair algae, not much coralline activity. My KH was kind of low so I fixed that up but it didn't make much difference. Anyway, a couple of weeks ago one of my light bulb T5's literally blew a hole in it. With one bulb not working the other doesn't work (I have the 36" Hagen Glo HO dual T5 fixture) and I had to order bulbs in, so the tank was about a week without much light, just a bit of filtered sunlight from the front door for maybe an hour a day max and otherwise ambient room light. But in that week I have seen more coralline algae growth than I think in the previous 6 months all together. I'm starting to wonder if I have TOO MUCH light even though obviously it's not that much compared to some tanks. Has anyone else noticed this? I wonder if I should raise my light fixture even more?

By the way I had an actinic bulb and a 10,000K bulb, but obviously at this point they were a couple of years old since I didn't replace them regularly, I didn't see the point. For the past week or so I have been running a new actinic white bulb (12,000K - 50% actinic 03 & 50% triband phosphor) along with the old actinic (blue) because I didn't want to shock things by going from total darkness to brand new bulbs. The other new bulb I have (besides the actinic white) is the Aquasun by UV lighting company which is a 10,000K bulb.

[Original Fin]

One thought...old fluorescent bulbs experience both diminished intensity/PAR, as well as color spectrum shift. The latter can have a profoundly negative impact on photosynthesis of different types of algaes and zooxanthellae, while at the same time having a positive effect of others, like nuisance hair algae.

I would replace the other actinic bulb too and see how that goes. Unfortunately, once HA gets a foothold in your display, as you know it is a very long process to begin to get rid of it.
I've found that a combination of the following has been an effective way to mitigate HA in my reef tank:
-The use of RODI water to eliminate introduced dissolved solids.
-The use of a macroalgae refugium to outcompete the HA for nutrients.
-The use of phosphate removal media.
-Try not to overfeed, but if you must, have either the appropriate CUC, or increase the volume/frequency of water changes to control nitrates.
-A photoperiod of not more than 12 hrs/day
-Maintaining magnesium levels that are in balance with cal and Alk.
-10x flow in gph/gal or better. (this is important for the spread of coraline)
-A skimmer rated for 2x the size of your tank or better.
-having a deep sand bed is a plus as a nutrient sink.
-I've had good luck with the use of Sea Hares. They eat HA like nothing else, but must be returned to LFS or paid forward to other hobbyists once the HA is gone. Otherwise they starve.

HTH

[Carissa]

I'll replace that other bulb today and see what happens. The hair algae has all but died off since I raised up the lighting so I'm not too worried about that anymore. I would just like to get some more coralline going.