Is my formula correct for Alk swing during water change

[ReefGoat]

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)  +  (12x4)  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. 

 

 

 

hypothetically 

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. 

 

 

 

 

 

 

 

[ReefGoat]

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. 

[mitten_reef]

1.  Why do you use 13, instead of 12 in your formula?

 

2.  If you worry about a big “swing”, space it out into 2 gallon wc twice a week?  Bonus is you’ll likely won’t have to worry about dosing after that for a while. 

but I also nearly nuked my tank play fast and loose with the alk, but we’re talking from 6 all the way to 10 and back, TWICE.  Corals can handle a bit of alk movement. Just make sure it’s inside the 7-9 range. 

[ReefGoat]

15 minutes ago, mitten_reef said:

1.  Why do you use 13, instead of 12 in your formula?

 

2.  If you worry about a big “swing”, space it out into 2 gallon wc twice a week?  Bonus is you’ll likely won’t have to worry about dosing after that for a while. 

but I also nearly nuked my tank play fast and loose with the alk, but we’re talking from 6 all the way to 10 and back, TWICE.  Corals can handle a bit of alk movement. Just make sure it’s inside the 7-9 range. 

fat finger mistake. It should be 12 you are correct. I will edit it. But it's really more the formula is even the right format to figure this out is what I was curious about. 

[ReefGoat]

In theory if my math is correct. My swing will only be from 8.9 to 9.4 which should only be a .5 swing. Again if my formula is even the right one to be using. 

[Murphs_Reef]

Next question. Why are you doing water changes? 

[ReefGoat]

2 hours ago, Murphs_Reef said:

Next question. Why are you doing water changes? 

Are you kidding? You dose a lot of stuff to keep trace elements in your water. I replenish my trace elements by doing water changes. Don’t start with me. Is the math correct or not?

 

I’ll just figure it out for myself and report back for anyone that ever stumbles across this 

[mitten_reef]

5 hours ago, ReefGoat said:

fat finger mistake. It should be 12 you are correct. I will edit it. But it's really more the formula is even the right format to figure this out is what I was curious about. 

Yes, the formula is correct. dKh is essentially a unit of concentration. 
your formula is solving Cfinal in a basic chemistry class. Where V1 is your remaining volume, V2 is your wc volume. 

(C1 x V1) + (C2 x V2) = (V1+V2) x Cfinal

 

you have to account for slight discrepancy of space/volume taken up by your rocks, as well as the space from waterline to the rim (tank volumes are usually rated to the rim height). It is the actual liquid volume that you’re looking to use in the formula. 

[mitten_reef]

So 18 and 22 may not be the most accurate. But it gave you a general idea. 

[Murphs_Reef]

5 hours ago, ReefGoat said:

Are you kidding? You dose a lot of stuff to keep trace elements in your water. I replenish my trace elements by doing water changes. Don’t start with me. Is the math correct or not?

 

I’ll just figure it out for myself and report back for anyone that ever stumbles across this 

Wow! That's a tasty response... Was asking a question! I'll leave you to it in future.   

 

And by the way trace won't replenish with just water change, macro possibly but micro... Nope.  

 

I by the way do a water change weekly to assist manage phosphate. I dose trace..... To replenish trace... And if you look at my recent post on my build thread... I Still struggle to keep up with trace consumption. 

 

Wouldn't it be easier to get a salt that mixes at a lower Alk? So you can mitigate the whole swing? 

 

Best of luck. 

[TheKleinReef]

[mcarroll]

17 hours ago, ReefGoat said:

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.

Personally, I suspect you're over-thinking it.  Unless you're running something like an Acro tank, most corals tolerate alk changes within the range you're talking about.  

 

But I'm generally a fan of over-thinking, so....

 

Why not re-standardize on IO's numbers?  That would be the logical route...plus it would give the tank more time between water changes before alk gets "too low" due to depletion by corals.

 

12 is not what IO will always mix to, BTW....should be more like 10.   I doubt that even this bucket will continue at the alk levels you're seeing.  If you haven't used much salt yet, it's not too late to re-mix the bucket, which should normalize things.

 

BUT, if you think it's really a bad bucket vs mixing, you should contact Marineland – if you're right, they will most likely send you a replacement bucket.  They have been good about this in the past.)

 

BTW, I think your math looks OK, but I'm no mathemeticain. 😉 

 

Also BTW, what salinity are you getting these readings at, and is your refractometer calibrated and tested?  (Do Ca and Mg levels seem right?)

 

As noted in an earlier post, your alkalinity is going to go from "slightly high" to "slightly higher" within the accepted 8-12 dKH range.  (I like to consider the range as 3.0-4.0 meq/L, or 8-11+ dKH....almost the same.)

 

If alk currently isn't too low, and you're doing only partial water changes, and your tank has normal NO3 and PO4 levels (ie. positive, not near-zero) then I don't think you have anything to fear from a small elevation in alk.   (And all those things seem to be true in your case.)

 

Caveat all this if you're running an Acro tank. 😉 

[TheKleinReef]

2 hours ago, mcarroll said:

your tank has normal NO3 and PO4 levels (ie. positive, not near-zero)

your ability to bring nitrate and phosphate into every thing you say is astounding lol

[Murphs_Reef]

1 hour ago, TheKleinReef said:

your ability to bring nitrate and phosphate into every thing you say is astounding lol

Fair enough on the lad phosphate is a beast of a weapon... To much or little will knock on to alk consumption... 

 

 

[TheKleinReef]

32 minutes ago, Murphs_Reef said:

Fair enough on the lad phosphate is a beast of a weapon... To much or little will knock on to alk consumption... 

 

 

unrelated to the original question tho. phosphate wouldn't have much of an immediate effect on the concentration change from a WC. how the alk responds long term afterwards may and does.

 

my comment was more of a meme since mccarroll loves to solve every single reefing problem imaginable on n/p or flow. which isn't always the case.

[Lebowski_]

19 hours ago, Murphs_Reef said:

Next question. Why are you doing water changes? 

I don't understand this question? Are you saying they shouldn't do water changes?

[Murphs_Reef]

14 minutes ago, Lebowski_ said:

I don't understand this question? Are you saying they shouldn't do water changes?

Na it was to find out for what purpose really. 

 

Some reefers do it to reduce nutrients, others with lightly stocked softie, lPS tanks get away with this to replenish kH, mg and ca..

Them some just seem to do it because thats what you should do...

 

38 minutes ago, TheKleinReef said:

unrelated to the original question tho. phosphate wouldn't have much of an immediate effect on the concentration change from a WC. how the alk responds long term afterwards may and does.

 

my comment was more of a meme since mccarroll loves to solve every single reefing problem imaginable on n/p or flow. which isn't always the case.

Ah right lol ok