Mixing Kalk In Kalk Reactor W/ Saltwater

[barrierreefcf]

Boomer,

I was following Bricky's post on RC in Randy's Chemistry Thread and before Randy could address the ? fully it seems as though the thread is gone. So I thought I'd pose the question here and see if you could help.


Could you please explain the chemical reactions and possible detriments involved in this scenario?

Using a geo kalk reactor with the feed pump directly in the sump and a ph controller set at 8.0 controlling the feed pump into said reactor. The effluent is allowed to only come out at a slow drip. Not sure of drops/min at this time but I can ask and find out. If the Ph drops below 8.0 in the system and kalk reactor starts dripping back into system as small amounts of system water is fed into the reactor. The reactor mixes twice daily controlled by timer. Bottom line is the kalkwasser is mixing with saltwater rather than fresh but most of it is getting a pretty long dwell time before returning to the tank. The only time the tank clouds is if the reactor is stirring at the same time the controller activates dosing. I believe Randy mentioned magnesium and calcium precipitating when you mix Kalk and saltwater but I never actually got to read any of his responses myself. Just heard second hand. If they do precip will the stirring/dwell time allow for them to dissolve back into solution in saltwater that is low in these elements or would the ph in the reactor prevent this? Understandably this scenario would be less efficient than mixing Kalk in freshwater but is there a chemical reaction that would harm anything or lead to imbalances?

Thank You,
Cy

 

[shallowreef]

Bump- I'm interested in this subject as well!

 

[DonW]

I can tell you from expeience that not properly mixing kalk will cause all sorts of precip all over everything. It wont fully disolve in sw so that should be about the same.

Don

 

[barrierreefcf]

But will it dissolve at all? Since its contained in a reactor does the precip matter other than needing frequent cleaning? Will certain elements be lacking in what is actually dosed to the tank because of the precip?

 

[Boomer]

As Don has pointed out it is a bad idea to mix seawater with kalk. Randy has mentioned this many times as have I and even others. The reactor water will produce a precip in the form of magnesium hydroxide and calcium carboante. Some of the hydroxide will go back into solution but the calcium carbonate will not. All of this can plug up the reactor and trun other thinks into a mess

Randy did reply and the post just went to a back page, just as they do here. Here is his full reply

Sure. I discuss many of them here in the context of adding limewater to tank water:

What is that Precipitate in My Reef Aquarium?
http://reefkeeping.com/issues/2005-07/rhf/index.htm


Some of the reactions would be:

HCO3- + OH- --> CO3--


that raises carbonate a lot, then it reacts with calcium and magnesium:

Ca++ + CO3-- ---> CaCO3

same reaction for magnesium and strontium, and also many other metals like iron.

Also,

Mg++ + 2OH- ---> Mg(OH)2,

which is insoluble.

The biggest noticeable problem would likely be a skewing of calcium and alkalinity, with calcium rising relative to alkalinity (due to Mg(OH)2 and MgCO3 formation).

 

[barrierreefcf]

Thanks!

So applied to this inefficient type of dosing:

1. The magnesium level should gradually fall, right? Would this be measurable w/ a Salifert test kit or would the test register the magnesium hydroxide as well?

2. Can calcium and alk be maintained at NSW levels or will the Magnesium gradually fall to the point where they cannot? I guess this may vary based on the particulars of the system.

3. If the equipment is maintained and the precip is dealt with in hoses/pumps does the fact that there is precipitation happening pose any threat to the aquarium inhabitants?

Sorry to be a pain! I read the article but still had questions.

 

[DonW]

I think you will find it a waste since you will only be adding very little alk and little if any ca. The precip on the sump walls, pumps and plumbing will be huge.

Don

 

[Boomer]

1. The magnesium hydroxide is not going to be in solution it is going to collect on /in the reactor and other places but some may be in suspension. Yes, you may be able to test for it. If particles of this are floating around it will/may skew you Alk and Mg++ readings.

2. When/if Mg++ falls it will be hard to keep up Ca++ levels.

3. Threat, no but it will mess you your water quality parameters and may give false readings, so threat in that sense then yes.

Finally, you are not going to really gain anything with this method. It will be a big headache

 

[barrierreefcf]

Thank you. I understand much more clearly now.

 

[Boomer]

Your Welcome