Simple explanation of calc, ph, alk relationship

[Ltspd]

I need a good simple, easy explanation of the relationship of ph to alk to calcium.

I seem to be battling these parms in my tank. I run a reactor, with a effluant of about 6.7ph and a steady drip rate.

My calc is about 380-390
My alk is about 9ish dkh
My ph is about 8.0

I need to raise the calc and ph, and keep the alk about where is at, I think..


Any help?

[Randy Holmes-Farley]

First, welcome to the forum:)

Second, those values are largely fine. If anything, it is the calcium that is low. It is lower than the natural seawater values of 410 ppm (as you probably realize).

The alkalinity is higher than natural seawater of 2.5 meq/L (7 dKH), and is about where many reefkeepers maintain it.

A pH of 8 is a tad on the low side, but my concern depends if that is the daily pH high, or the daily pH low. If it is the low, there is nothing to be concerned about. If it is the high, you should try to raise it, IMO. Reactor tanks tend to run low pH without it being a problem.

Raising calcium with calcium chloride would be a somewhat desirable thing for you (IMO).

<< I need a good simple, easy explanation of the relationship of ph to alk to calcium. >>

OK, now to the relationship in as simple of terms as possible (we can ramp up the complexity as long as you find it interesting).

Calcium (Ca++) and carbonate (CO3--) are both present in the tank.

If you get too much of either or both floating around, they stastically run into each other "too often", and insoluble calcium carbonate (limestone) forms.

Alkalinity in seawater is largely composed of bicarbonate (HCO3-) and carbonate(CO3--). As alkalinity increases, these chemicals increase.

Bicarbonate and carbonate are related to each other by pH: as the pH rises, bicarbonate is converted into carbonate. As the pH lowers, carbonate is converted into bicarbonate.

So, as the alkalinity rises, the amount of carbonate rises, making it more likely that calcium carbonate will precipitate.

As the pH rises, the amount of carbonate rises, making it more likely that calcium carbonate will precipitate.

So having high alkalinity at high pH is a double whammy, making calcium carbonate more likely to precipitate.

Likewise, low alkalinity at low ph is also a double whammy, making it more likely that the calcium carbonate skeletons of corals will actually dissolve.

[Ltspd]

First, welcome to the forum

Thank you.

Second, those values are largely fine. If anything, it is the calcium that is low. It is lower than the natural seawater values of 410 ppm (as you probably realize).

Yes, I realize that I need levels up and around 410-420. I currently have clams, SPS and such and they are all doing fine. I just want to give them the proper amounts of what they need.

A pH of 8 is a tad on the low side, but my concern depends if that is the daily pH high, or the daily pH low.

My high for the day is 8.12 per ph probe (calibrated) and the low is 7.99. This was measured at the end of the light period for the high and when I got up in the morning for the low. The low has the sump/refig lights on. I have read where Kalk water will help maintain the ph on the higher side,or closer to 8.3. Would a kalw water drip be recommended?

OK, now to the relationship in as simple of terms as possible (we can ramp up the complexity as long as you find it interesting).

Ok, now I am going to make some even simpler comments, please let me know if I am correct.

* Too mcuh Ca++ and Co3-- will produce a snow storm for lack of a better word (precipatate) in the tank. Calc levels above 500 I have heard will do this.

*As Alk increases so does the Ca++ and the C03--. So higher Alk means Higer Calc.

* A ph of 8.3 is ideal, and this level balances the conversion of Bicarb (Hc03-) and Carb (Co3--)

*Higher Alk means more Hco3- and Co3--, which throws the ph out of ideal

* High Alk plus high ph casue the calc (Ca++ & C03--) to also be too high making the snow storm.

* Low alk plus low ph actually draws calc (Ca++ & Co3--) from the corals. Which is the basic principal behind a calc reactor, the reverse of what we want in the tank.

One last question, comment. What are ideal levels?

I was under the assumption that Ph should be 8.3, Calc should be 420 and Alk should be 10+ dkh.

Thanks for the help!

[Randy Holmes-Farley]

Paul:

I have read where Kalk water will help maintain the ph on the higher side,or closer to 8.3. Would a kalw water drip be recommended?

Limewater will help raise the pH, if you want to do so. Your pH values look fine to me.

As Alk increases so does the Ca++ and the C03--. So higher Alk means Higer Calc.

That's only true if you are adding calcium and alkalinity together. You can raise and lower calcium and alkalinity independently , if you want to. As alkalinity rises, so does carbonate.

A ph of 8.3 is ideal, and this level balances the conversion of Bicarb (Hc03-) and Carb (Co3--)

Seawater has a pH of 8.2. Anyone recommending something other than that is expressing an opinion that at least some people won't share. While my tank often has a pH above 8.2, that's simply because I use limewater. Others use CO2/CaCO3 reactors and have a pH much like yours. There no strong reason to believe that one is better than the other.

There is an exact relationship between bicarbonate and carbonate based on pH, but I'm not sure what 'balanced' means.

Higher Alk means more Hco3- and Co3--, which throws the ph out of ideal

It means more of both HCO3- and CO3--, but that is to some extent independent of pH (since many tanks are not at equilibrium with the air, if they were, the alkalinity alone would determine the pH; in tanks this often isn't so).

High Alk plus high ph casue the calc (Ca++ & C03--) to also be too high making the snow storm.

Snowstorms are highly unsusual events. Even slightly elevated calcium and alkalinity can cause slow precipitation of CaCO3 on things like heaters. Again, high alk and/or pH can help lead to precipitation, but it doesn't raise calcium. They do raise carbonate.

Low alk plus low ph actually draws calc (Ca++ & Co3--) from the corals. Which is the basic principal behind a calc reactor, the reverse of what we want in the tank.

Yes. The pH and alk have to be fairly low for that to happen, but it can.

One last question, comment. What are ideal levels?

That's really an opinion question, but here's mine:

Calcium: about natural levels, 410 ppm.
pH: about natural levels of 8.2; 8.0 to 8.4 is fine
alkalinity: about natural levels to slightly higher (2.5 meq/L to 4 meq/L; 7 to 11 dKH)

[Ltspd]

Randy, thanks a bunch :)

I got it, or atleast have it better than I did ;)

I am pretty good on levels, with calc being my low point. I have been adding turbo calc (calicium chorlide?) and will slowly bring my level up. I feel that once I achieve that level the reactor will maintain it just fine.

I may look at a additional Kalkwater drip to help the ph maintain the 8.0+ level it should.

Once again, thanks!

[Randy Holmes-Farley]

I have been adding turbo calc (calicium chorlide?) and will slowly bring my level up. I feel that once I achieve that level the reactor will maintain it just fine.

That's what it is, and that sounds like a good plan:)

[biggdriver]

On my container of Kent Marine Kalk it says That kalk is the original method of adding calcium to a reef.
Why won't this be all that is needed..I thought I had it now you have me confused.
WOn't this also keep a buffer for the alk?
I am using ro water..shouldn't this be all I need to keep up these levels?

[biggdriver]

If I understand this right then . Adding calcium via Kalkwasser will not necessarily buffer my water. But if you add a buffer to raise the alkalinity won't the calcium level go up on it' own. THis process doesn't work in the reverse? If kalk is added then a buffer is also needed. WHat is the buffer composed of? WOuld make sense to say it contains some form of calcium?

[Randy Holmes-Farley]

biggdriver:

Limewater is a perfectly balanced additive for calcium and alkalinity. I hope that I did not write anything to the contrary.

Paul want's to raise calcium without raising alkalinity. You cannot do this with limewater: it will raise both.

I hope that this explanation sorts things out.


Adding calcium via Kalkwasser will not necessarily buffer my water.

No, it will raise alkalinity. Many people refer to this as buffering the water. That's a somewhat incorrect usage, but I think it is what you mean.

THis process doesn't work in the reverse? If kalk is added then a buffer is also needed. WHat is the buffer composed of? WOuld make sense to say it contains some form of calcium?

Nothing besides limewater is needed unless you are correcting some type of pre-existing problem.

[biggdriver]

One more thing. Does Kalk(powder form) go bad..I found a large Full container sitting around. And I think it is almost 7 yrs old. It was opened and a little bit was used but it was shut tightly and no moisture got into it. The Peter Wilkens Brand not that it matters what brand.. I bought new stuff anyway but would like to know if it is safe to use or not.

THanks

[Randy Holmes-Farley]

If CO2 from the air penetrates the container, it will go bad. If not, it won't. Going bad just means some extra CaCO3 around that won't dissolve. If you let the solids settle out, it will be OK, but you won't be sure how saturated it is unless you measure it somehow. Conductivity is a good way (about 10 mS/cm for saturated limewater).