White caps on Botrycladia red grapes

[JoJosReef]

There have been some white caps appearing on my Botrycladia red grapes over the past few weeks:

I was initially wondering if it was going sexual, but it doesn't seem that the grapes are completely going white and losing consistency. Instead, the white caps seem to be hard. Is this like a Ca precipitate on the grapes? I don't notice white deposits anywhere else (but also consider, might be hard to see anywhere else).

Any thoughts? Some parameters:

Sg: 1.025 (down from normal 1.026)
Alk: 7.6 (Red Sea)
Mg: 1710ppm (Salifert; yes, that's right and test is consistent with Red Sea...been running in the high 1600s for many months due to weird batch of HW salt)
Ca: somewhere between 500ppm and 530ppm (Red Sea, harder to tell than Salifert since color changes more slowly)
NO3: ~4ppm (Salifert)
pH: ~8.3


@Subsea have you seen this before?

 

[Subsea]

Very nice.

I just received some sprigs of red grapes in a red macro grab bag from live plants that had something similar. I prefer subdued lighting. In general, red macro has a more complicated life cycle than greens & browns.

 

[Subsea]

When I get Bortacladia from the divers, it is a dark burgundy as it is collected in 15’ to 130’ of water. Light intensity is subdued. If subjected to intense light, it will photo shock and loose flotation berries.

Note color difference between shaded red grapes on left side and grapes in back middle of tank.

RED MACROALGAE (RHODOPHYTA)​

The genus Rhodophyta is the largest and most diverse group of tropical and temperate marine algae with more than 2,000 species worldwide. Their dominant pigment is phycoerythrin, which gives off rich shades of red, orange and blue. Red macro algae are some of the most varied and striking of all marine algae and are highly sought after as aquarium specimen.