what could be causing burning tips

[Reef Pilot]

Which acros did you get burnt tips on? I haven't had that with alk swings, but have seen that for two other reasons. And it only affected "skinny" acros, like birdsnest, red dragons, and some others.

One is lighting, if acros were moved to an area where the light was too bright too quickly, tips were bleached. Moving them down, or to a partially shaded area solved that.

And the other is leaving them out of the water too long. My frag rack is out of the water during water changes, and if I leave it too long without bathing them occasionally, the tips can be burnt (birdsnest are most vulnerable to this). Also, has happened when I left them on the table too long while fragging. Clipping off the tips helps with faster regrowth.

I run bio pellets, and my alk runs between 7 and 9, most of the time. Fluctuations happen due to doser adjustments and sometimes water changes. Have hit 10 a few times, but mostly it is around 8. SPS is doing very well. The only time (last summer, and fall) that my SPS got hit, is when my phosphates got too high (when I combined sumps). But that again only affected some of them (like the more delicate deepwaters), with slower growth and some color loss. Once the phosphates were down, growth and color returned.

[asylumdown]

Ugh, well I cut way way back on my dosing of alk but the problem has continued. and today my alk measured by hanna is 8.96 and my alk measured by red sea is 9.2. I'm afraid that this has caused my corals to shut down and now even a reduced amount of dosing is causing the levels to creep up.

Reef pilot - the affected corals haven't been moved in 1-2 years and I've been running the same lights since I set up the tank.

It's affected about 60% of my acros at this point, a few of my montis, and I have another colony of SPS that looks like an Acro but I think is in a different genus that is one of my largest pieces that I think I'm going to lose completely. Mostly it's just the tips, but it's also causing the tissue around the polyp cups on a few species to swell, making them look like they're smooth. I'm afraid I might start losing entire colonies.

The other thing I've noticed since I fixed my BP reactor (which is still a PITA for maintenance BTW) and switched to the high capacity GFO is that I'm no longer getting any film algae on my glass and the light dusting of dinos that's waxed and waned on my sand bed for well over a year has completely and totally disappeared. My sand is as white as the day I put it in again.

Can damage this severe alone be caused by alk over 8 in a low nutrient, BP run tank, or could a sudden and precipitous drop in nutrients by itself have caused these issues?

I'm not sure what else to do now. I don't want to do a water change because the salt I'm using at the moment mixes up to around 9dKH, and I'm afraid to cause any more sudden shocks by taking either the GFO or the BP offline. Other than cutting the amount of bicarbonate I dose back even further, is there anything else I should do?