ALK and Calcium Increasing Without Dosing

Biokabe · Oct 5, 2020

Can alkalinity and calcium increase without dosing?

I recently added a Trident to my tank - definitely one of the better purchases I've made. When I first added the Trident, I noticed that my ALK and Calcium, especially, were low. I wasn't surprised by this, as I hadn't been dosing either of them - my dosing pump had started going out and I didn't trust it to dose appropriately. So I started dosing above-replacement levels to get those levels up into the "good" ranges. Started at just over 300 ppm on calcium.

Eventually, my ALK got up in to the 11 range, and Calcium was nearing 500 ppm, so I discontinued dosing on both of them to let them fall down into a lower range (8-9 for Alk, 420-460 ppm for Calcium). Since then, there's been a bit of a drop-off in both levels, but they've fallen into a pattern that, frankly, perplexes me.

Nowadays, my Alkalinity will fluctuate between 9.2 and 9.5, and my calcium between 430 and 450. So not dangerous numbers by any means - in fact, they're pretty much where I want them to be. But if I'm not dosing them - shouldn't those numbers just go down, rather than alternating? Are there other explanations for those parameters to fluctuate? Could my Trident need calibration?

Just want to make sure I'm not ignoring a warning sign.

Randy Holmes-Farley · Oct 5, 2020

Top off is what?

Water changes?

Declining nitrate or nitrate dosing (both boost alk).

9.2 to 9.5 and 430 to 450 up and down may just be test error, with no real increase or decrease.

Biokabe · Oct 5, 2020

Top-off is RO/DI with a Tunze Osmolator.

I haven't done any water changes since I started noticing this, was planning on doing one tonight (not as a corrective issue, just as part of regular maintenance).

I haven't been dosing nitrates, but I have been more diligent as of late about harvesting chaeto from my refugium, and I think my nitrates have gone down as of late - I've never had massive algae growth in this tank (other than persistent cyano on the sandbed), but I've noticed that what I have had has decreased.

One thing that has changed over this time is a noticeable drop in the average PH. Earlier in the summer, with the windows open a good chunk of the time, the PH would average about 8.15 (highest I saw was 8.35, lowest 8.06, with about a 0.2 swing within each day). Starting about three weeks ago, however, the wildfires down in California and Oregon forced us to keep our windows shut pretty tight, and the average PH dropped to about 7.8 (high of about 8, lowest point was 7.5, but the average swing was 7.9 - 7.7). There are some coral skeletons in the tank - would it be at all likely for the lower PH to somewhat dissolve those skeleton and liberate the elements into the water?

Randy Holmes-Farley · Oct 6, 2020

There is a very small and steady dissolution of sand deep down where bacterial action lowers the pH to the point where dissolution of calcium carbonate can begin. Long time reefers occasionally have to add sand because of this. in some cases, that will prop up alk and calcium when demand is very low.

Most likely, you just have very low demand for whatever reason right now.

Biokabe · Oct 6, 2020

Randy Holmes-Farley said:
There is a very small and steady dissolution of sand deep down where bacterial action lowers the pH to the point where dissolution of calcium carbonate can begin. Long time reefers occasionally have to add sand because of this. in some cases, that will prop up alk and calcium when demand is very low.

Most likely, you just have very low demand for whatever reason right now.

Thanks... a little less baffling now. =) I like to make sense of things when they don't make sense. Low demand is probably it, coupled with those background fluctuations you were talking about. I don't have many fast-growing stony corals right now, so for now I'll just hold steady and resume dosing when I notice the levels start to drop.