Coralline algae growth exploded, now turning brown

[Necrodaemus]

A couple months ago, I had an explosion of purple algae growth….completely covered the back glass, overflow, powerheads, and areas I don’t regularly scrape. The past few weeks, it is turning dark brown in large areas….the brown cannot be easily brushed off without scraping the glass clean. Any idea on what or why this is happening? I’ve attached photos of before and after.

 

[rawrsean]

Coralline algae utilize a large amount of Iodine and Magnesium, along with a healthy amount of nutrients. It sounds to me like a deficit. Coralline grew until it ran out of something. What are your tank parameters?

Has anything changed or fluctuated recently? Coralline algae does not respond well to changes, and sometimes dies off in response, even if the change wasn't necessarily bad.

 

[Necrodaemus]

Coralline algae utilize a large amount of Iodine and Magnesium, along with a healthy amount of nutrients. It sounds to me like a deficit. Coralline grew until it ran out of something. What are your tank parameters?

Has anything changed or fluctuated recently? Coralline algae does not respond well to changes, and sometimes dies off in response, even if the change wasn't necessarily bad.

Parameters are:
8 dkh
420 Ca
1380 Mg
pH 8.3 (8.0 at night).
5 NO3
0.1 PO4
System is maintained with a daily dosing of All For Reef. Not sure if anything has fluctuated aside from nutrients. NO3 had been dropping down to barely readable in testing but I was able to get it back up to 5 by reducing the photo period of the chaeto in the refugium.

 

[rawrsean]

If your nitrates really fell below 5 ppm, I would surmise this to be a primary cause. A drop in nutrients is a viable cause of coralline die off. Coraline really enjoy a detectable level of nitrates.

 

[Necrodaemus]

If your nitrates really fell below 5 ppm, I would surmise this to be a primary cause.

Very well could be. I test NO3 with Salifert and the reagents are still well within date. It was testing at 1-2ppm (had to hold the vial sideways to even see a slight pink color).

 

[Lavey29]

Coralline will again cover the dead parts when conditions are preferable for it.

 

[deome]

I have a frag tank that had some really pretty algae growth--purple on bottom half of glass, pink on top half. One day I increased the lighting for all my tanks, and within a week all the pink algae went brown and then bleached white (purple on bottom half unaffected). Nitrates were and still are very detectable.

Your two photos almost look like you made a lighting change. Did you?

 

[Necrodaemus]

I have a frag tank that had some really pretty algae growth--purple on bottom half of glass, pink on top half. One day I increased the lighting for all my tanks, and within a week all the pink algae went brown and then bleached white (purple on bottom half unaffected). Nitrates were and still are very detectable.

Your two photos almost look like you made a lighting change. Did you?

No changes to lighting at all.