Alkalinity and Lanthanum Simultaneous Dosing/Offset Dosing

[GotCrabs]

Good afternoon.

Question: Is there a rough ratio I can use to dose alkalinity at the same time as I dose Lanthanum?

Why? I have an Apex with BRS dosers and intend to inject LC into the skimmer as needed to control Phosphates. I've experimented with it and it seems to work. But yes...the Alk gets messed up. If I can dose a corresponding amount of Alk at the same time under the same program...it's a win. The alk would be in addition to the daily dosing of Alk. (I'm not worried about the programming as I think I have that figured out.)

What are you using?

• Phosphate E from Brightwell. Probably move to Seakleer if I need to keep using it. That remains to be seen.
• BRS 2 parts Soda Ash using a gallon jug with a single dose bag. (Which means I have no idea what the concentration is in my gallon jug.)

What I think I understand... (Please correct if I'm wrong.)

1. A dose of LC consumes both phosphates and carbonates. Carbonates = Alkalinity. Therefore Alkalinity goes down.
2. The amount of each that gets consumed depends on their relative ratios to each other at the time of dosing.

So the answer is likely a function of the phosphate and alkalinity measurements at that moment in time.

What I would love to see...assuming it makes sense...is a few ratios with typical phosphate and dKH values.

If this doesn't exist, maybe there's some math someone can share and I can make the chart?

If that's too hard or asking too much...a rough starting point or a range might be useful.

Thanks in advance for those who can provide guidance.

 

[Randy Holmes-Farley]

I'm not sure there's a ratio fixed enough to be useful in this context. It will certainly depend on phosphate, alkalinity, pH (maybe more so than alk), the localized amount of lanthanum while the reactions are still happening, and the mixing rate.

Think of it this way...

Suppose lanthanum reacts faster with phosphate than with carbonate. Even if it is infinitely faster, it will deplete phosphate locally as it mixes in, and then leave mostly carbonate to react with. That's the mixing part and will be super hard to quantify.

Lanthanum actually reacts with PO4---- and CO3--, not other forms (HPO4--, HCO3-, etc.). THe amount of those depends on phosphte concentration, alkalinity, and pH. Both exist more at higher pH, but I'm not sure which is increasing faster as the pH is raised. It may depend on both the starting pH and the amount the pH rises. Further, the local precipitation of either lanthanum phosphate or carbonate will lower pH locally.

So, IMO, you might generate a ratio empirically for you exact system and way of addition, etc, but it will not directly translate to other tanks.

 

[GotCrabs]

I'm not sure there's a ratio fixed enough to be useful in this context. It will certainly depend on phosphate, alkalinity, pH (maybe more so than alk), the localized amount of lanthanum while the reactions are still happening, and the mixing rate.

Think of it this way...

Suppose lanthanum reacts faster with phosphate than with carbonate. Even if it is infinitely faster, it will deplete phosphate locally as it mixes in, and then leave mostly carbonate to react with. That's the mixing part and will be super hard to quantify.

Lanthanum actually reacts with PO4---- and CO3--, not other forms (HPO4--, HCO3-, etc.). THe amount of those depends on phosphte concentration, alkalinity, and pH. Both exist more at higher pH, but I'm not sure which is increasing faster as the pH is raised. It may depend on both the starting pH and the amount the pH rises. Further, the local precipitation of either lanthanum phosphate or carbonate will lower pH locally.

So, IMO, you might generate a ratio empirically for you exact system and way of addition, etc, but it will not directly translate to other tanks.

As always, a detailed response I can chew on. Thank you Randy.

Bottomline for me: I’ll just have to “add some” Alk. Maybe double my daily to start. Seems better than just adding it later.

If I may, I’d like to thank you for all the fabulous insights you’ve provided the reefing world. I dare say without them we would not be reefing with as much confidence or success. Thank you.