CA Reactor Effluent

[gpodio]

I have a question regarding effluent levels of a calcium reactor. I made a reactor from a canister fitler ( link (http://reefcentral.com/forums/showthread.php?s=&postid=12243544) ) and I'm waiting for a PH meter to arrive in order to test the effluent PH which is lower than my current test kit is capable of reading.

Without a PH controller (constant CO2 rate) and using bubble and drip rates within a 'popular range', can we assume that KH and PH of the effluent have a somewhat linear relationship?

For example, at 20bpm & 20ml/min, the effluent KH is 11dKH. My target is around 30dKH. Could one safely adjust the CO2 rate to obtain 30dKH in the effluent without necessarily testing PH?

Thanks

[Randy Holmes-Farley]

I personally would not use a pH controller on a CaCO3/CO2 reactor. I'd perhaps measure pH, but I would not want a pH meter to control the flow of CO2.

I would not assume that the pH is anything remotely close to liner with CO2 added.

Alkalinity may be closer as long as you are within the range where CaCO3 is actually dissolving.

Finally, however, if the effluent alkalinity is only 11 dKH, it is certainly safe to consider raising the CO2, as long as there is good internal mixing in the reactor. :)

These have more:

Calcium Reactor setup calculator (CaCO3/CO2 reactors)
http://home.comcast.net/~jdieck1/reactor.html

A Guide to Using Calcium Reactors
http://www.reefkeeping.com/issues/2002-05/sh/feature/index.php

[gpodio]

Thanks Randy. I was indeed referring to a linear relationship between PH and KH of the effluent, sorry for the confusion.

I don't plan on using a controller for this setup, just wanting to get closer to target values while I wait for delivery of the new PH meter (just a Hanna handheld). I only have KH and Alkalinity tests to go by until then...

So far I don't see any buildup of CO2 in the canister but I'll keep an eye on it as I raise CO2 rate.

Thanks again

[Randy Holmes-Farley]

I would not assume any particular relationship between pH and dKH. Once you drop the pH to the point where the solid CaCO3 starts dissolving, the alkalinity will go up with more CO2, but the pH may not drop much more.

Good luck. :)

[David Grigor]

That is how I always tuned a reactor by ALK levels not by PH.

It is trial and error in the beginning to determine what the effluent alkalinity needs to be to maintain your system. While keeping the effluent rate constant, you should be able to determine though by mapping your tank Alkalinity and your effluent alkalinity of a week or two time period.

For example ( as ever tank will be different ) on my 320g show, I knew that 28dkh effluent kept my show tank around 10dkh. So if during my weekly testing of the tank alkalinity, if it changed I would then test the CA effluent then make adjustments as necessary.

[gpodio]

Interesting... so past a certain point, how can more CO2 increase dissolution of CaCO3 without bringing PH down further?

I am looking forward to kicking my Kalk addiction ;-)

[David Grigor]

It can't, that's what they do.

No kicking the Kalkwasser habit, kalkwasser is a complement to CA reactor becuase CA reactor will supress tank PH from the increased CO2. It's just a necessary evil.

[Randy Holmes-Farley]

Well, I disagree a bit, but perhaps we are talking about different points.

If the pH is about 6.5, where CaCO3 is dissolving, and you add more CO2, the pH will not drop much, but more CaCO3 will dissolve. The dissolution of CaCO3 tends to raise the pH, offsetting the pH drop that the CO2 addition would have caused.

I agree that there is a limit that CO2 can attain, but if you are not yet at that limit, more CO2 can result in higher alkalinity but not in appreciably lower pH in the reactor effluent. :)

[gpodio]

That makes sense. But still, PH can mistakenly be brought lower than 6.5 so it's not like it would be completely countered by the extra CaCO3 being dissolved... right? Perhaps the relationship becomes more-so exponential? I mean it's impossible to have a PH6.5 and a KH4 for example right?

Not trying to contradict you :-) Just trying to understand the relationship, if one exists. See I was expecting to find that at PH6.5 for example, alkalinity of the effluent would be on average around a certain level. Therefore allowing one to safely adjust their CO2 rate solely based on effluent alkalinity or carbonate hardness.

Sorry for all the questions :-)

[Randy Holmes-Farley]

My point is that any dissolution of CaCO3 has a huge pH raising effect inside of the reactor, and that offsets the drop when adding more CO2. The pH drops pretty fast into the mid 6's as you add a little CO2, and then drops relatively little beyond that even with a lot more CO2.

You were asking about the relationship between pH and alkalinity, and that is why I was suggesting that at a certain pH, where CaCO3 is dissolving, there is not much of a relationship. Yes, as you add more CO2, the pH will go down a little bit more. Perhaps you will detect that and perhaps not. It is essentially like adding an acid to a strongly buffered solution. There is a drop, but not anything like what you find in an unbuffered solution at the same pH. It may, in fact, but nearly unnoticeable. It is definitely not linear.

IMO, you can use the pH as an initial guide to get into the right range, and then use the alkalinity of either the effluent or, preferably, the tank itself to fine tune the CO2 addition. Using pH is not optimal, IMO, for that tuning.

[gpodio]

So in conclusion, it's quite easy to get the PH to the mid 6', after that the raise in alkalinity makes it a lot harder to go further. In my reasoning I wasn't really taking into consideration the effects on PH the extra carbonates would have.

I'm going to increase bubble rate until I get an effluent KH of around 20-25, after that I'll wait for the PH meter to arrive.

Thank you for your patience!

[kae]

Does using calcium reactor really cause tank pH to be lower? I think it should be higher because of higher alkalinity.

Does CO2 buildup in a reactor reflect the improper tuning?

Thank you.

[Randy Holmes-Farley]

Does using calcium reactor really cause tank pH to be lower? I think it should be higher because of higher alkalinity.

Does CO2 buildup in a reactor reflect the improper tuning?

It delivers CO2 to the tank along with the alkalinity, and that effect tends to drive the tank pH lower. Even perfectly tuned, there is no way around that.

So in conclusion, it's quite easy to get the PH to the mid 6', after that the raise in alkalinity makes it a lot harder to go further. In my reasoning I wasn't really taking into consideration the effects on PH the extra carbonates would have.

Yes.

Your plan sounds like a fine one. :)

[kae]

One of my friend had higher tank pH after runing calcium reactor (Schuran). Why?

Thanks.

[Randy Holmes-Farley]

If you boost the alkalinity substantially and also have very good outgassing of the CO2 (via aeration with normal air), then a reactor can raise pH indirectly through raising of the alkalinity. But most often, then effect is downward, rather than upward. :)

[kae]

<a href=showthread.php?s=&postid=12247730#post12247730 target=_blank>Originally posted</a> by Randy Holmes-Farley

It delivers CO2 to the tank along with the alkalinity, and that effect tends to drive the tank pH lower.

Excess CO2 that was delivered to the tank is in what form, CO2 gas or carbonic acid?

Thank you very much. :)

[Randy Holmes-Farley]

Both probably, and also just as an imbalance of HCO3- relative to CO3-- in the effluent. In all cases, blowing off enough CO2 solves the "problem".

2HCO3- ---> CO2 + CO3-- + H2O

[BradR]

So glad I read this thread. Was waiting on a controller to control reactor pH but now am just going to be testing reactor and tank alkalinity. One thing I was worried about was in my old reactor the coral gravel media "melted" and didn't want that to happen again. Maybe this is unavoidable, dunno.

[Randy Holmes-Farley]

Measuring the pH may be able to prevent that from happening, but manual CO2 control along with pH measurement should suffice, and completely manual control with no pH measurement can work, but may take a bit more (and more careful) trial and error. :)