Will using a UV lamp inhibit coralline algae growth?

Oceansize · Jul 29, 2015

I know a UV lamp will inhibit cyano, green algae, etc, that's why I'm using it. But will it also inhibit the growth of the purple/blue calcareous coralline algae that we want?

Randy Holmes-Farley · Jul 29, 2015

You mean the usual inline UV's?

I wouldn't be convinced it will hurt any of those, good or bad.

Oceansize · Jul 29, 2015

Yes, it's inline. I was not convinced either (which is why I was content to leave the bulb burnt out the last several years). But my experience over the last week has profoundly changed my mind. Normally when my nitrates get up to 15 ppm or so I experience a cyano bloom. This weekend, still unable to reduce the bloom, I replaced the bulb and my cyano disappeared overnight. I checked my nitrates at that time and they were 20 ppm. I'm just shaking my head that I have nitrates at 20 ppm and no cyano. That's unheard of for my tank. I am glad of this because I want some nitrates for coral growth, but I wish cyano didn't come with. So far this has been a great solution for allowing me to have some level of nitrates without accompanying cyano. The caveat is if it inhibits the purple/blue stuff I wish would compete better with the cyano.

Randy Holmes-Farley · Jul 31, 2015

I don't think it will inhibit the spread of coralline very much. :)

luke33 · Jul 31, 2015

IME I have no issue growing coralline with a UV running. I have the pink/purple all over the place.

Oceansize · Jul 31, 2015

Getting a magnesium test kit was one of the last things I got around to doing. When I did finally get one, I was alarmed to see my magnesium down in the low 1100's. So I immediately got some magnesium to bring the level back up to 1300-1500. It is now in the low 1400's and I swear the purple coralline is finally spreading instead of shrinking.

And this is at the same time that the UV is running. This might indicate that the UV doesn't do much, yet yet I know the UV does affect my cyano, it can't be coincidence that the bloom literally disappeared the day after I replaced the bulb for the first time in five or six years.

Interesting to note how magnesium has such a profound effect on coralline algae, when magnesium is so often one of those overlooked parameters.