50% RODI, 50% calcium reactor effluent (alk test)

[salty joe]

If I were to dilute my calcium reactor effluent 50-50 with RODI water, could I double the value given for a fairly accurate alkalinity reading?

 

[ndrwater]

No sure why you would want to do this, but... The Alkalinity reading coming from the CaRx should be substantially higher than your targeted Alk. You are not only maintaining the Alkalinity lever in your tank, but also replenishing what is takes up by the corals.
Best practice is to know what you Alk level is prior to the CaRx, know where you want to be, and adjust the reactor accordingly either through effluent flow, or CO2 injection rate.

 

[KrisReef]

I'd say yes, but I'd probably be wrong. There are a lot of competing ions in seawater that fresh water dilution probably would skew your results.
Use half tank water (known Kh) and 1/2 effluent, and I suspect the error would be less (or the results closer to accurate.)

(I know just enough chemistry to be dangerous and to mix proper martini's)

 

[salty joe]

The reason I check the effluent Kh as I dial in the reactor is, I can see what's happening a lot faster as I change the CO2 bubble rate. The last effluent Kh was under 16. Instead of waiting an entire day to not see the Kh in the tank change by much, I increased the bubble rate right then. I can do that every couple hours. My low target for Kh effluent is 30. I imagine I'll end up closer to 40. Also, knowing the Kh value at a given bubble rate when the reactor has fresh media should help me know when to change or add media. I plan on keeping the flow consistent.
Of course, I keep my eye on the tank's Kh.

Can someone with chemistry knowledge definitively tell me if adding half RODI to calcium reactor effluent will yield fairly accurate results if the given value is doubled?

 

[Randy Holmes-Farley Verified Community Expert]

If I were to dilute my calcium reactor effluent 50-50 with RODI water, could I double the value given for a fairly accurate alkalinity reading?

Yes.

 

[salty joe]

Thanks!

 

[Randy Holmes-Farley Verified Community Expert]

Thanks!

You're welcome.

Happy Reefing.

 

[mattfish]

Yes.

Randy , are you sure on this ? i contacted Hanna about there ALK checker, being that its max range is 20 DKH , and i too want to check KH in the effluent , There reply was -- The checkers are based on sea water curve , and by using RODI too dilute it will trow off the results.

 

[Randy Holmes-Farley Verified Community Expert]

Randy , are you sure on this ? i contacted Hanna about there ALK checker, being that its max range is 20 DKH , and i too want to check KH in the effluent , There reply was -- The checkers are based on sea water curve , and by using RODI too dilute it will trow off the results.

100 % sure it is a valid procedure for normal titrations. I expect it is true of the Hanna as well, but I am not 100% certain since they do not reveal its details.

I discuss here how the alk of a mixture is the weighted average of the two solutions (under alkalinity facts), and the only minor point is a small change in the true endpoint, but that is insignificant in this context.

Chemistry and the Aquarium: What is Alkalinity?

Chemistry and the Aquarium: What is Alkalinity? - Randy provides an overview of alkalinity as to why it's important, how it's measured, and how can it be tested.

reefs.com

 

[JMetaxas]

I use this method (50% RO/DI water and 50% Calcium Reactor effluent) and trust the results.

 

[Randy Holmes-Farley Verified Community Expert]

Randy , are you sure on this ? i contacted Hanna about there ALK checker, being that its max range is 20 DKH , and i too want to check KH in the effluent , There reply was -- The checkers are based on sea water curve , and by using RODI too dilute it will trow off the results.

You can easily check how far off it may be by taking some high alk salt mix (say, 11-12 dKH) and do a 50:50 mix and see what you get.

 

[mattfish]

100 % sure it is a valid procedure for normal titrations. I expect it is true of the Hanna as well, but I am not 100% certain since they do not reveal its details.

I discuss here how the alk of a mixture is the weighted average of the two solutions (under alkalinity facts), and the only minor point is a small change in the true endpoint, but that is insignificant in this context.

Chemistry and the Aquarium: What is Alkalinity?

Chemistry and the Aquarium: What is Alkalinity? - Randy provides an overview of alkalinity as to why it's important, how it's measured, and how can it be tested.

reefs.com

Thanks for replying , i trust your judgement , i feel confident it is correct too.

 

[mattfish]

You can easily check how far off it may be by taking some high alk salt mix (say, 11-12 dKH) and do a 50:50 mix and see what you get.

makes sense, thanks