Why reducing alk dosing and increasing Ca dosing have the opposite effect?

[clown99]

1.5 year-old Biocube 29, probably 26g of water. Last week, these were the parameters:
NO3: 0.5ppm
PO4: 0.01
Alk: 11.2 (Salifert)
Alk: 10.2 (Hannah)
Ca: 390
Mg: 1350
pH: 8.34
Temp: 77.6
Salinity: 1.025

So I reduced the alk dosing from 13mL/day to 11mL/day and increased the Ca dosing from 13mL/day to 14mL/day, expecting the alk to be lower and Ca to be higher.
One week later, these are the parameters:

NO3: 0.5ppm
PO4: 0.01
Alk: 12.1 (Salifert)
Alk: 11.1 (Hannah)
Ca: 340
Mg: 1290
pH: 8.36
Temp: 77.5
Salinity: 1.025

I don't understand why the results are opposite from what I would expect. What is going on here?

 

[Euphyllia97]

My guess is that your calcium dosing is actually dissipating in the water instead of dissolving. Due to the high alkalinity. Alk, cal and mag are constantly looking for a stable natural ratio.

I would try to stop dosing calcium and alk. Letthe alkalinity come down naturally to a value of 9dkh. When you reach 9dkh try to keep that value stable and determine how much calcium you still need to add once it has established. When your alk comes down, I wouldn’t be surprised that you calcium will raise automatically without dosing to a good value.

 

[clown99]

Thanks. I'll try this & report back.

 

[Randy Holmes-Farley Verified Community Expert]

1.5 year-old Biocube 29, probably 26g of water. Last week, these were the parameters:
NO3: 0.5ppm
PO4: 0.01
Alk: 11.2 (Salifert)
Alk: 10.2 (Hannah)
Ca: 390
Mg: 1350
pH: 8.34
Temp: 77.6
Salinity: 1.025

So I reduced the alk dosing from 13mL/day to 11mL/day and increased the Ca dosing from 13mL/day to 14mL/day, expecting the alk to be lower and Ca to be higher.
One week later, these are the parameters:

NO3: 0.5ppm
PO4: 0.01
Alk: 12.1 (Salifert)
Alk: 11.1 (Hannah)
Ca: 340
Mg: 1290
pH: 8.36
Temp: 77.5
Salinity: 1.025

I don't understand why the results are opposite from what I would expect. What is going on here?

Maybe you changed the wrong ones. lol

There is no normal explanation other than test error or water change effects.

 

[Randy Holmes-Farley Verified Community Expert]

My guess is that your calcium dosing is actually dissipating in the water instead of dissolving. Due to the high alkalinity. Alk, cal and mag are constantly looking for a stable natural ratio.

I would try to stop dosing calcium and alk. Letthe alkalinity come down naturally to a value of 9dkh. When you reach 9dkh try to keep that value stable and determine how much calcium you still need to add once it has established. When your alk comes down, I wouldn’t be surprised that you calcium will raise automatically without dosing to a good value.

That cannot be an explanation, sorry.

Dissipating does even have a meaning here that i can understand, but precipitation of calcium carbonate would lower both alk and calcium. Since he reduced alk dosing, alk must decline if the effect involved reduced dosing and increased precipitation.

 

[Euphyllia97]

That cannot be an explanation, sorry.

Dissipating does even have a meaning here that i can understand, but precipitation of calcium carbonate would lower both alk and calcium. Since he reduced alk dosing, alk must decline if the effect involved reduced dosing and increased precipitation.

Precipitation is what I meant indeed. (Sorry non-native)

 

[clown99]

Would raising Mg help?

 

[Randy Holmes-Farley Verified Community Expert]

Would raising Mg help?

I don't see any evidence of precipitation or, frankly, any real problem. Just keep slowly tweaking the doses to get where you want calcium and alk to stabilize.

magnesium is perfectly fine at 1290 ppm, but if you want to raise it for some reason, it is also fien to raise it.

 

[clown99]

I found yesterday that the dosing hose for Calcium is floating in the bottle. So Ca has not been dosed ...!!
I stopped the Alk dosing and did a 10% water change. Will test every day for Alk, Ca, Mg.