Alk/CA dropping like a rock even with dosing

[CaptainOver]

I've been wrestling with this for a while. My ALK/CA seem to be dropping impossibly fast. I keep upping my dosing times, but they seem impossibly long now. I feel like I'm overdosing, but my ALK hovers around 5.5-7 and I have trouble trying to raise it.
Medium stocked tank with SPS frags and some larger LPS colonies.

Tank: Red Sea 350 (~75g water)
Trident testing
BRS 2 part (7.5 min/hr)
BRS dosing pumps (~2ml/min)
ATO with saturated (or close to it) Kalk (~1 gal/day)

1 gal per day of Kalk should provide 1.5 dkh ALK.
360ml/day of ALK should provide 6.5 dkh ALK (!?!).

I've assumed I must be causing precip by overdosing, but every time I stop all of my dosing to get a level set, I panic when I see the ALK tumble. For instance, I stopped dosing at 6PM tonight (other than Kalk/ATO which only ran once for a few seconds) and 3 hours later my DKH dropped from 6.3 to 5.6. But earlier in the day I was dosing the full 360ml/day (+ATO) and ALK still dropped from 7.1 to 6.3 in 6 hours.
I'm stumped...

 

[Nanoreefboi]

This is really strange. Try dosing even more?! I mean you only have little sps frags. I’m stumped

 

[CaptainOver]

That's what I say to myself every time...Just a little more and it will stabilize. But it doesn't.
I've scraped the coraline off the back glass to get rid of that as a sink, but it didn't really help. All the rocks are covered with coraline, though, so that's certainly a source for some consumption, but not that much.

 

[Nanoreefboi]

Are your corals growing insanely fast? How long are you running your lights? A longer photo period could make corals calcify faster

 

[Mykawl]

Magnesium?

 

[BeejReef]

You're running a ferrari to my ford escort, but I went through something similar recently. In my case, 72g of total water volume, a few softies, a couple sps frags, and a dozen lps frags/small colonies were consuming (apparently) almost 3dkh per day.

Is your magnesium level up to par? Assuming it is, you may have to stop all dosing for a full 2-3 days, if you're dealing with the classic precipitation scenario. The alk/calc has to get low and stay low for a little bit for the existing precipitant crystals to sort of seal up and stop sucking it out.

 

[Silver14SS]

Maybe try another test method to confirm the results you are getting are correct. If you stopped dosing and the lights are still on there will still be alk consumption.

 

[CaptainOver]

Maybe try another test method to confirm the results you are getting are correct. If you stopped dosing and the lights are still on there will still be alk consumption.

I had these same results before I got the trident - using Hanna checker for ALK.
I stopped dosing this morning again, at 8 AM before the lights came on full, and it dropped from 6.03 to 5.5 in 4 hours.
I just can't imagine my tank is actually using this much ALK...it is a ton. 360ml/day in 75 gallons of water is enough to offset 7dkh of consumption.
Using that 4 hour test as "evidence" would imply I'm consuming 3 dkh per day. So maybe the rest is precipitating? I can try setting my doser to 3 dkh equivalent and see how it does...

 

[Silver14SS]

You positive the BRS 2 part and Kalk ATO are at the dKH you expect? Maybe try a new batch of Alk supplement mixed to a known strength and use only RODI water for ATO to get a new baseline of Alk consumption?

 

[BeejReef]

I'm over my head on this one

This is what I saw and looks like it could apply to you. You're dosing over twice as much as they are on a 160g well established tank.


also, is your kalk and 2 part dose hitting the sump in a really high flow area? I put a $20 china powerhead in the sump for just that reason. It keeps my chaeto tumbling too.