As many of you know, I'm a total SPS newbie, with only two in my tank and never any in my life before. The two I have is a red plating montipora and a branching Seriatopora (seriatopora caliendrum).
When I got them both, they were small frags, but with my powerful LED lighting and fast water flow (around 50x), and high reef levels, calcium 450, alkalinity 12, low phosphate, etc, they were growing noticeably each week.
Then my Seriatopora started to strip, that is, the polyps started to disappear, leaving the pure white calcium carbonate base exposed. It got worse like a disease eating it away until now, I'd suggest 40% of it is gone.
I've never had SPS before and never experienced corals dying back like this, and there didn't seem to be any cause, but after much research I'm pretty sure I've found the cause.
Stripping from the base upwards seems to be stability related, specifically alkalinity stability, while sps stripping from the tips could be lighting or flow related, and stripping all over could be bacterial/disease related.
It kind of makes sense, as currently, I'm dosing once per week, which I was never totally happy with, but not bothered about it enough to do anything about it, as it didn't seem to be causing any issues. Little did I know...
Every Saturday, I'd measure my reef levels (I say reef levels meaning the typical alkalinity, calcium, magnesium, phosphate readings) and they were very predictable, the calcium level would drop to about 410, the alkalinity would drop to 7 dKh. I'd then measure out the 80g of sodium bicarbonate and mix with RO (and calcium chloride for calcium, but separately) and I'd dose them probably in thirds with several hours in between. So by Sunday evening, the levels would be right back up at 12dKh and 450ppm.
My only concern was that throughout the week, growth rate would slow because the levels are diminishing. I hadn't thought that the slow decline of the levels through the week, and the sudden increase over the course of the weekend would be too wild a swing to cause problems for the SPS, afterall, they were growing fine, and very quickly up until a few weeks ago...
I'm very soon to get a Cheap MC-03-M Peristaltic Dosing Pump
which has 3 heads, it's not an expensive one, but should do the job. I can then maintain the levels rather than dosing them, which will keep the parameters much more stable, which should prevent my SPS stripping any further.
In time, now I'm dosing daily rather than weekly, the SPS should stop dying back and start to continue to grow. The dead portions won't ever regrow, but growth should grow over the dead parts, but it can take a very long time...
Lesson learned, and let's hope I'm right!