Sanity Check on Understanding Alkalinity Changes

[mythesis]

New to reefing, about 3 months in. 90 gal tank, Live rock start & deeper sand bed.

Question: Why would KH be going up without dosing for it?

Background:

I use the Instant Ocean Purple Box mix for salt, mixed to 1.025 salinity (checked & confirmed by 2 LFS). Did a 10 gal water change last weekend (10/05).

About 2 weeks ago, my Nitrates & Phosphates dropped to 0 (about the same time the Diatoms were clearing up). I added the RedSea AB+ for 2 days, once at a higher dosage (3/4 of the ULNS dose) , and then the second day at a lower dose (1/2 of the ULNS dose). I also let the Skimmer cup drain back into the Sump rather than extracting anything. I haven't been running a filter sock at all for a while.

Thankfully, nutrients went back up, and I'm skimming as normal again.

3 new small fish (Royal Gramma, Link's Goby, Court Jester Goby, all from Biota, so roughly a 1", 2", 1" in size) were added this week after the nutrients were back to normal. Additional clean up crew (2 dozen snails, plus a ton of tiny cerith snails, 1 conch) were added recently as well.

So, does all that explain why my KH levels would be rising? I think they're getting to a "good" level, I just want to understand what's going on.

I test Nitrate, Phosphate, KH via Salifert. Calcium is via API. (I'll readily confess my color-matching is unreliable on Nitrate/Phosphate, so those numbers may not be fully accurate). But KH is a lot easier to tell and I'm surprised to see it climbing so much.

I keep salinity at 1.025.

Other than the two injections of AB+, I don't dose any chemicals.

 

[Randy Holmes-Farley Verified Community Expert]

A few possibilities.

1. Test error/variability.
2. Declining nitrate boosts alk.
3 water changes can boost alk if the new salt water is higher in alk.
4. Rising salinity will boost alk.
5. Tap water can contain alk.


There are other, slower effects that are not likely here, such as slow dissolution of sand.

 

[mythesis]

1. Seeing a consistent increase over the last month or two, not a 1-off test.
2. Definitely saw Nitrates drop from 20-40 down to 10 or less around the same time, so that is likely
3. Maintaining same mix (and test the Salinity before I do the change)
4. Keep testing salinity, and haven't seen changes
5. I assume this means Tap water? I do run a 5 stage RODI when mixing.



*OH* One thing I didn't think of --- I recently bought a new batch of salt mix. It is the Purple *bucket* instead of the Purple Box w/ bags. Is there any chance that would have an effect? (I assumed box & bucket were the same, but maybe just a different batch and/or brand-new mix vs. a bag that had been opened for a little before mixing?)


(edit: as always, thanks a ton for helping us newer folks understand the chemistry of our tanks. It's more than a little overwhelming and you're an excellent guide)

 

[Randy Holmes-Farley Verified Community Expert]

I’d just keep watching it. Have you tested the salt mix? It is likely higher than your tank, which is fine, but will always boost alk a bit.

The alk is fine even if it rises more.

You’re welcome!

 

[mythesis]

I’d just keep watching it. Have you tested the salt mix? It is likely higher than your tank, which is fine, but will always boost alk a bit.

The alk is fine even if it rises more.

You’re welcome!

Yes, I tested it at 1.025 before adding it to tank.

I'll keep an eye on things for sure.

 

[Randy Holmes-Farley Verified Community Expert]

Yes, I tested it at 1.025 before adding it to tank.

I'll keep an eye on things for sure.

What about the alkalinity of it?

 

[apeshot]

Yes, I tested it at 1.025 before adding it to tank.

I'll keep an eye on things for sure.

I think the suggestion is to test the new water for alk and ph (not just salinity) before you put it into the tank. That way you’ll know how the new batch of water will affect you in the display. Be sure to get the new water up to display temp temperature also since lower temps affect results also.

 

[mythesis]

What about the alkalinity of it?

Oh, duh, good point. I just assumed mix=mix. I can test that later today, thanks.

 

[mythesis]

What about the alkalinity of it?

Alk of the new water tested today at 9.7 . The water has sat in a Brute trashcan in garage since I mixed it last week. Temps in the high 70's most of the week.