Moving ALK, how fast is too fast?

[oblio]

After reading the thread "the secret to colorful,healthy corals....obvious to some,elusive to many " I felt it might be a positive change to lower my ALK levels, have been hovering around 10 for the last couple of years. Over the last 3 weeks I have lowered it to 8.9, My corals don't look bad, but they don't look as happy as they did three weeks ago. Everyone is just a bit closed up, maybe to say they are about 85% extended would be more helpful. I have a Yellow fiji that is about 12" in diameter and now for the last 3 days he has been without any polup extension. He has done this in the past but not for 3 full days that I can recall.
A common theme on the forum is keeping the ALK steady, my question is, how fast would you think you could move this single parameter?
All other measurable parameters seem to be as expected,
Salinity 1.026
Nitrate - 0
Phosphate - 0 ( the AP kit, would like to get the hanna one day)
PH - 8.1
Calcium 440
Mag - 1320
Alk 8.9

Thanks for any input here

 

[thegrun]

I've read that alkalinity changes should not exceed 0.5 dKh per day. I haven't seen any research to back this up, but it seems like a reasonable number. You are well below this threshold; I suspect the corals are just needing to adjust to the new parameters.

 

[Reefvet]

... have been hovering around 10 for the last couple of years. Over the last 3 weeks I have lowered it to 8.9, My corals don't look bad, but they don't look as happy as they did three weeks ago. Everyone is just a bit closed up, maybe to say they are about 85% extended would be more helpful. I have a Yellow fiji that is about 12" in diameter and now for the last 3 days he has been without any polup extension.

10 dKH isn't high. In fact you'll find a lot of people targeting that level to increase growth. You may find more color at lower alkalinity but there's no guarantee of that.

And more importantly, if it's not broke why try to fix it ?

I'd suggest if your corals look good then go by what you see and don't chase numbers. From what you're describing after lowering your alkalinity it sounds like your system was doing well at the higher level and your corals are not happy with the change.

 

[Randy Holmes-Farley]

These are complicated issues, but I do not think there is any simple correlation between color and alkalinity at least not one that is reproducible tank to tank.

There is an apparent correlation between colors of some corals, and the zoox levels in them (which are usually golden brown). Reducing nutrients a lot can sometimes reduce zoox levels and so some corals look more colorful even if the coral tissue is unchanged.

BUT, such ULNS systems seem to have a sensitivity to higher alkalinity levels, for reasons which have never been explained (IMO). That seems to apply mostly to SPS, FWIW.