Where does the ALK go?

[brians_224]

Hi - thanks for your time!

I've been battling an ALK roller coaster lately. I started to test daily when I started to fun a phosphate reactor - discontinued its use 8 days ago. I still can't maintain an alk level higher than 8. Where does the ALK go? I'm dripping 1/2 gallon of rodi water with 5-6 teaspoons of disolved baking soda a night in affeort to raise it. I top off with mrs wages pickling lime. CA is 425 - 450. Its been a battle to maintain this CA level as well, but not as hard as the ALK. My MG level is ~ 1100.

I recently added 5 SPS frags, and fragged a Xenia colony. I've also got a bit of an algae problem - are there any algaes that consume calcium and Alk?

Where is all my ALK going?

 

[Randy Holmes-Farley]

This is a 45 gallon tank?

How high does the pH get at the end of the light cycle, or the end of the limewater addition?

 

[brians_224]

yep - 45 gallons. ALk should be through the roof right?

The PH seems pretty constant at 8.0 - tested with lights off. I have a refugium that I keep lit 24x7.
The top off is via a tunze osumlator(sp?) - so the top off is through out the day.

 

[Randy Holmes-Farley]

Yes, if you are really adding the much baking soda (5-6 teaspoons dry baking soda dissolve din a larger amount of water, and not adding baking powder or some other thing), then it should rise by about 2.5 meq/L each night. That seems like a hugely excessive amount to add anyway.

It is likely precipitating as calcium carbonate.

What happens to the alkalinity if you add none of the baking soda?

 

[brians_224]

If I don't add it, the tank seems to stay at 8. I have a total volume of 60 gallons. I'm definitely adding baking soda and not baking powder.

Any realtionship to this and my algae battle - its kind of like hair algae but much coarser, and rougher, kind of feels brittle.

I kept increasing it per our previous discussion - previous posts.

 

[TwistedTiger]

Re: Where does the ALK go?

<a href=showthread.php?s=&postid=6925076#post6925076 target=_blank>Originally posted</a> by brians_224
Hi - thanks for your time!

I've been battling an ALK roller coaster lately. I started to test daily when I started to fun a phosphate reactor - discontinued its use 8 days ago. I still can't maintain an alk level higher than 8. Where does the ALK go? I'm dripping 1/2 gallon of rodi water with 5-6 teaspoons of disolved baking soda a night in affeort to raise it.
Where is all my ALK going?

My alk plunged when I started using phosban and I also discontinued after a week, but have had trouble maintaining ever since, about 3 weeks.

 

[Randy Holmes-Farley]

So the alk stays at 8 dKH regardless of whether you add it? Maybe the kit is not working?

Has calcium been decreasing during that dosing?

What salt mix?

8 dKH is a fine value.

 

[brians_224]

I've got two salifert test kits one old and one new - i've tested one against the other and they both measure the same. If I measure the ALK in the morning after dosing - it measures 10-11. The alk seems to be consumed during the day. I was trying to get a higher level to increase coralline covereage. I have little coralline growth.

Calcium has been decreasing as well.

 

[Randy Holmes-Farley]

Do you see much precipitation on pump impellers or heaters?

 

[jwedehase]

Could it be that with such a low magnesium level, the alk/ca storing capability of the water is hindered? And with Ca that high, there isn't much room left for alk? I've always understood this very basic illustration, gleamed partially from Calfo:

Consider a mixing bowl that can hold 100 marbles. You have red marbles for Ca, and blue for Alk. You can put in 100 marbles, in any combination. The goal is 50/50 (or whatever). If you add 10 calcium marbles, then 10 alk marbles are going to overflow (precipitate).

I've also understood magnesium to represent the size of the bowl, roughly. So in this case, the bowl is pretty small, with such a low magnesium count, and it's very filled with calcium already, with such a high calcium count, not leaving much room for alk.

Am I even close to oversimplification?

 

[Randy Holmes-Farley]

:thumbsup:

Yes, low magnesium can lead to excessive abiotic precipitation of calcium carbonate.

That's why I asked about precipitation. Regardless, it wouldn't hurt to raise it, and it might help. I usually recommend 1250-1350 ppm for magnesium.

FWIW, I don't care too much for Anthony's explanation. It implies that there is a simple upper limit to the amount of calcium and alkalinity, and that isn't true.

Magnesium works by binding to crystals of calcium carbonate that have started to form, ruining them for further precipitation. It thus allows the levels of claciuum and alkalinity to rise more before reaching the same amount of precipitation.

 

[brians_224]

Yeah - there's hard stuff building up on my titanium heater and in my sump - but its not coraline. I've also have to clean my panworld pump about once a month because it seizes due to build up.

 

[Randy Holmes-Farley]

OK, then I'd try raising the magnesium, keeping the pH from getting too high during the day (and during the dosing with high pH additives), and keep the alkalinity at the lower end of normal (say, 7-9 dKH).