Varying Alk Levels

[Michael Gentile]

Hello all,

So I have recently started dosing. In preparation for this I tested with Hannah checkers weekly every Sunday for a month to see how much my corals were consuming. With no water changes. My calcium and mag do not need dosing at this time. So I started with Alk with was at 8.5. after finding out how much they consumed over the course of three weeks I dosed the alk up to 11.5dKH (which matches my salt). I only have to dose 1ml a day to maintain my tanks consumption currently. Yesterday I did a 5 gallon water change for a 60 gallon system. When I tested the alk today, it was at 9.5dKH, I tested again right after and got 9.6dKH.

Is there something I am missing? according to my salt (Red Sea Reef Pro) at a specific Gravity of 34.0ppt the KH is 11.5.

Any advise would be great i do not want to do anything drastic right now!

Tests Dates	Calcium	Adj Calcium level	Alkalinity	Adj Alkalinity	Magnesium
1-9-2022	475ppm/461ppm		8.5dKh		1400ppm
1-16-2022	464ppm		8.2	Started dosing 11.3ml per day foundation B	1410ppm
1-23-2022			10.8
1-24-2022	446		11.5		1410
1-29-2022			9.5/9.6

 

[AJsReef]

When first implementing dosing, testing at a weekly interval is insufficient to calculate dosage.

I would stop dosing and test Alk daily, at the same time, for a period of 7 days and then determine your dosage.

That said, with a 60 gallon system and only an 11ml a day consumption I wouldn’t anticipate seeing much change.

 

[Randy Holmes-Farley Verified Community Expert]

I'm not sure I'd be dosing anything yet. 11.5 dKH is a pretty high target.

A 5 gallon water change of 9.5 dKH water with 11.5 dKH salt mix will only boost the alk to 9.65 dKH.

 

[Michael Gentile]

I'm not sure I'd be dosing anything yet. 11.5 dKH is a pretty high target.

A 5 gallon water change of 9.5 dKH water with 11.5 dKH salt mix will only boost the alk to 9.65 dKH.

Could you explain how this works out to be 9.65?

 

[Randy Holmes-Farley Verified Community Expert]

Could you explain how this works out to be 9.65?

Sure.

When combining fluids, the final alkalinity is the weighted average of the two solutions.

You are combing 5 gallons of 11.5 dKH and 60 gallons of 11.5 dKH.

The weighted average is [5 x 11.5 + 60 x 9.5]/65 = 9.65 dKH

 

[Michael Gentile]

Sure.

When combining fluids, the final alkalinity is the weighted average of the two solutions.

You are combing 5 gallons of 11.5 dKH and 60 gallons of 11.5 dKH.

The weighted average is [5 x 11.5 + 60 x 9.5]/65 = 9.65 dKH

Interesting, maybe i will just aim to keep it there then, since i have a mixed reef, I don't need high levels, i was just trying to match my salt for water changes!

 

[EricR]

Sure.

When combining fluids, the final alkalinity is the weighted average of the two solutions.

You are combing 5 gallons of 11.5 dKH and 60 gallons of 11.5 dKH.

The weighted average is [5 x 11.5 + 60 x 9.5]/65 = 9.65 dKH

Negligible difference in this example but since it's 60 gallons total, wouldn't "changing" 5 gallons of the water be:

(5 x 11.5 + 55 x 9.5)/60 = 9.67 (((negligible difference in this case)))
???

*only checking in case I try to use the formula on a higher % water change

 

[Randy Holmes-Farley Verified Community Expert]

Negligible difference in this example but since it's 60 gallons total, wouldn't "changing" 5 gallons of the water be:

(5 x 11.5 + 55 x 9.5)/60 = 9.67 (((negligible difference in this case)))
???

*only checking in case I try to use the formula on a higher % water change

Yes, you are right. I mistakenly though it was a 65 gallon system.