Check my math? Calculating my Alk Swing with water change water.

[GatorGreg]

Tank is 22g and the water change amount is 4 gallons. My running Alk is 8.9 and for whatever reason my current bucket of Instant Ocean is mixing up right around 12. Here is the math I am using to figure out my anticipated Alk swing if I do nothing to lower the Alk for my water change water and just do the water change without lowering it to my running tank level.

I googled around for a while and found some old dated threads from a couple different sites. This is the formula that I think may be correct but I just want to make sure.

(8.9x18) + (13x4) divided by 22

= 9.4dkh after water change




I know I can use muratic acid to lower it but I am weary to use it because I can only find it in the pool section at hardware stores and I don't want to risk it having something else in it geared towards pools (cleaner, algicide etc.). In theory if I could find the correct muratic acid I think the math for that would be.


3.1 x 4 x .123 = 1.5ml of muratic acid to lower my water change water to 8.9 from 13


are the formulas I am using for these two instances correct? Or am I way off base here.

 

[GatorGreg]

I wanted to add that the reason that I run the tank at 8.9 just dates back to the salt that I was using whenever I first started the tank. I discontinued using that salt once I ran out because one it was expensive and two I had to order it off the internet. The Instant Ocean is cheaper by almost half when I'm ordering online at Petco and picking up very near my home. It's just way more practical and economic for me. But I decided to still run my tank at the same Alk as it has been since the start. If the Instant Ocean mixes up to 12 consistently I don't think I'd ever want to run my tank that high anyway. So I'm trying to figure out my options here