Alk readings going all over the place

[MBX5]

So I'm at a loss on getting Alk stable in my nano. I've been testing for the last three days and getting these readings. I'm using this http://reef.diesyst.com/flashcalc/flashcalc.html to calculate how much Randy's recipe to use. Testing is done with Redsea Pro
3/22/16
Salinity 1.25
Alk 9pm 7.0 raised to 8.4 with 7.7ml of Randy's
Ca 9pm 445
Mg 1460
3/23/16
Salinity 1.25
Alk 9pm 7.6 raised to 8.4 with 9ml of Randy's
Ca 9pm 440
Mg 1460
3/24/16
Salinity 1.25
Alk 9pm 6.4 haven't raised it yet
Ca 435
mag 1450
My Ph runs from 8.1 am to 8.23 pm
I'm trying my best to get a baseline of dosing throughout the day but it seems to use different amounts each day? Thanks for any help you can offer. Just retested with a Salifert Alk kit and getting the same numbers.

 

[Downbeach]

Are you using any type of pH buffer? Using RO/DI water?

 

[Eckolancer]

How old is the tank? That's a lot of alk to be using in a day how much coralline algae and hard corals do you have? How much water is in the setup?

 

[Randy Holmes-Farley Verified Community Expert]

Is the second number in these sentences measured or calculated?

Alk 9pm 7.0 raised to 8.4 with 7.7ml of Randy's
Alk 9pm 7.6 raised to 8.4 with 9ml of Randy's

 

[MBX5]

The tank is about 2 months old with 6 frags and a few lps. Coralline isn't growing on the glass yet but I do have about 5lbs of live rock and 10lbs of base from BRS. Water is made with R/O I am running media carbon and GFO. The number raised to was a test number after letting the dose mix in for a bit. I was actually shooting for 8.3 on the first one but got .4 so kept that as a target for the next day.

 

[Randy Holmes-Farley Verified Community Expert]

My suggestion is to try adding a fixed amount each day, such as 1.5 dKH, and see what that does for you, rather than adjusting every day.

 

[MBX5]

Thank you Randy I'll give that a try and keep my eye on things.

 

[MBX5]

Okay one last thing. My Alk is now holding at 8.6 with Randy's recommendation. I'm about to do a 4 gallon water change on my 20 Gallon nano and the IO is reading 11ish. Is that okay or do I need to bring it down before adding? If I do what's the best way to do that? Thanks again

 

[Randy Holmes-Farley Verified Community Expert]

A 4 gallon change of 20 gallons total will raise alk from 8.6 to 9.1 dKH.

That is OK, but if you do nott want to to rise, you can dose less alk that day, or add acid to the salt mix to drop the alk,

FWIW, that rise is generally not a problem for creatures, unless it is a ULNS tank.