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notsofishy
07/28/2008, 06:55 PM
In the past I have used Crushed coral in my top off water for calcium levels it seemed to work well as my ro water came with a ph of about 6.4 however now I am just dosing kalk and was wondering if having my water buffered by the crushed coral before gong to the kalk would be an issue?

jansenwrasse
07/28/2008, 06:58 PM
The crushed coral would have no effect on the potency of the Kalkwassar. Just use strait Kalkwassar ;)

tmz
07/28/2008, 11:37 PM
I don't understand why your ro water is at 6.4 ph. Nonetheless, f it dissolves the crushed coral it provides calcium and carbonate. Kalkwasser (Calcium hydroxide) will add these as well with a ph of 12.4 when fully saturated.

notsofishy
07/29/2008, 12:05 AM
yea im not really sure why its that acidic either. but to clarify what I was going to do is leave cc in the resovoir in my sump so that the water going from my top off is slightly buffered. Then I will also be pumping a fixed volume of water from that same resovoir to a kalk reactor which doesnt seem to be a problem. Thanks for the advice. Also what does most RO water ussually run at in terms of PH?

MCsaxmaster
07/29/2008, 05:29 AM
1) "Pure" water will normally have an acidic pH due to the dissolution of small amounts of CO2 and the production of carbonic acid from that CO2. It would take an unusual situation (e.g., elevated gaseous ammonia) to counteract that effect.

2) A normal pH probe cannot measure the pH of very pure water (= very low ionic strength) accurately. If you stick a pH probe in very pure water, you'll get a number on your meter, but that meter doesn't remotely correspond to the pH of the water--that takes specialized equipment ;)

3) In equilibrium with an atmosphere with pCO2 = 380 uatm the pH of pure water will be 5.66. Of course, pCO2 = 380 uatm is yesteryear ;) At 660 uatm you'll have a pH of 5.54.

Chris

notsofishy
07/29/2008, 07:18 PM
hmm interesting i figured it was dissolved co2 also for your notation pCO2=380uatm is that reffering to the co2 pressure in the atmosphere? Sorry for the questions but im about to continue my chem classes and need to review a little.

MCsaxmaster
07/29/2008, 08:01 PM
In this context, "p" refers to partial pressure, e.g., pCO2, pO2, pN2 are the partial pressure of CO2, O2, and N2.

notsofishy
07/29/2008, 09:10 PM
partial pressure! thats the word i was tryin to remember thanks for the review.

tmz
07/29/2008, 09:12 PM
<a href=showthread.php?s=&postid=13043742#post13043742 target=_blank>Originally posted</a> by MCsaxmaster
1) "Pure" water will normally have an acidic pH due to the dissolution of small amounts of CO2 and the production of carbonic acid from that CO2. It would take an unusual situation (e.g., elevated gaseous ammonia) to counteract that effect.

2) A normal pH probe cannot measure the pH of very pure water (= very low ionic strength) accurately. If you stick a pH probe in very pure water, you'll get a number on your meter, but that meter doesn't remotely correspond to the pH of the water--that takes specialized equipment ;)

3) In equilibrium with an atmosphere with pCO2 = 380 uatm the pH of pure water will be 5.66. Of course, pCO2 = 380 uatm is yesteryear ;) At 660 uatm you'll have a pH of 5.54.

Chris Thanks for the information. I knnew ro/di water would absorb CO2 but had no idea the ph would be that low.

MCsaxmaster
07/29/2008, 09:22 PM
Without any buffer capacity, the addition of even a very small amount of acid or base has a big impact on pH. The pH of RO water doesn't impact tank pH in any significant way. pH is not a conservative property afterall.

notsofishy
07/29/2008, 11:48 PM
I wonder why more people dont buffer the top off with cc its a bit easier than kalk

mixed_reefer
07/30/2008, 12:39 AM
Could a person push DI water through a fluidized reactor filled with CC and have a cheap calcium reactor? It almost seems like it might work if im understanding things correctly, use the effluent as topoff? What would the pH be like on the output of the reactor i wonder? Interesting stuff!

tmz
07/30/2008, 09:13 AM
<a href=showthread.php?s=&postid=13050105#post13050105 target=_blank>Originally posted</a> by MCsaxmaster
Without any buffer capacity, the addition of even a very small amount of acid or base has a big impact on pH. The pH of RO water doesn't impact tank pH in any significant way. pH is not a conservative property afterall. :) Thanks again, Not sure what "ph is not a conservative property,afterall"..." means. Could you clarify?

MCsaxmaster
07/30/2008, 11:26 AM
If you mix solutions together, some properties in the final solution will correspond to a weighted average of the solutions you mixed. For example, if you mix 1 L of sea water at 35 ppt with 1 L of freshwater you'll get a solution with a salinity 17.5 ppt. If the alkalinity of the seawater was 2.3 meq/kg and the freshwater has 0 meq/l you'll have 1.15 meq/kg. These are conservative properties.

If the pH of the seawater above was 8.20 (in equilibrium with the air) and the pH of the freshwater was 5.62 (in equilibrium) you won't end up with a pH of 6.91, which is halfway in between, you'll end up with a pH of 8.33 immediately after mixing and of 8.03 when the solution comes to equlibrium with the air. The pH varies depending on the properties of the solution. Hence, pH is not a conservative parameter.

tmz
07/30/2008, 09:28 PM
Thankyou

notsofishy
07/30/2008, 10:16 PM
<a href=showthread.php?s=&postid=13051088#post13051088 target=_blank>Originally posted</a> by mixed_reefer
Could a person push DI water through a fluidized reactor filled with CC and have a cheap calcium reactor? It almost seems like it might work if im understanding things correctly, use the effluent as topoff? What would the pH be like on the output of the reactor i wonder? Interesting stuff!

Thats what I originally planned on doing however I got lazy. Im sure it would work alright and with regular wc could sustain a light calcium load. However the results would be pretty limited the water wont stay at that low of a ph for long unlike a cal reactor. Ive been meaning to through some cc in with my topp off and test it a few days later. Im goin to mexico tommorrow though so it will have to wait.