Alkalinity correction for high CYA

[nater]

I remember some postings on the old forum about a correction factor for TA if you have high CYA. So far, my searches here haven't turned up much.

Does anyone know the accepted correction factors? I've worked my CYA down from 130+ to the 90-100 range and want to be sure I'm not running TA too low. The ring around my light shows some corrosion, but it may be from low pH over the winter.

Here's a range for my test #'s for the season so far:
pH: 7.2-7.8 (average of 7.4 over time)
FC: 8-15 ppm (average of 10 ppm)
TC: 8-15 ppm
TA: 80 - 120 ppm
CH: 190
CYA: 90-100
Salinity: 3000-3300 (Autopilot SWC)

I've been aerating quite a bit lately too help cool the water, so I add 4lbs of Baking Soda a week to keep the TA in that range. I also add about a gallon of acid every two weeks for pH control.

Any danger of being in a corrosive state due to my high CYA?

Thanks!

[waterbear]

'quick and dirty' estimate (that is pretty darn close!) is to subtract 1/3 of your CYA if your pH is 7.4-8.0 and 1/4 of your CYA if your pH is 7.0-7.2 from you TA. This will get you within a few ppm of the adjusted TA done by the mathematical formula. With your CYA as high as it is I would not let the unadjusted ALK fall below 110 and would run it as high as 140 ppm at a pH of 7.4 or higher!