How to raise Alkalinity? It won't go up...

[JFD]

Hi all,

I have a 200 gallon SPS dominated tank (with a couple of large colonies and then a few smaller one along with some frags - mainly acroporas) also, I have a refugium with 20% of the size of the tank with Chaeto.

I use a Calcium reactor and I've been trying to raise my alkalinity for a few days and regardless of the volume set the outlet it stays at 7.2/7.3 and in fact is slowly dropping...

The CaRx outlet alk is around 25 dKH and I have set it to 60ml/min after the Alk starting to drop with it at around 35ml/min.

My Mg is at 1560
Ca - 400
pH - 8.0

Any views on the reason for this?

Thanks and best,
Jose.

 

[Randy Holmes-Farley Verified Community Expert]

You may be getting close to the max for your reactor. When you upped the flow rate, what happened to alk? Can you raise it more? How are you controlling CO2?

 

[JFD]

You may be getting close to the max for your reactor. When you upped the flow rate, what happened to alk? Can you raise it more? How are you controlling CO2?

Hi Randy,

Thanks for replying, really appreciate!

I have a Vertex RX-C 6D which I think it is rated for up to 260 gallon and transparently my tank is not that heavily stocked (it is probably lightly to medium stocked), so wouldn't expected this to be the case... The CO2 is being controlled by my Apex and a solenoid, also I'm using a Kamoer fx-stp so, yes I could raise it more. However, I think I found the problem...

As I was reading your post, I've noticed precipitation in the form of some light cloudiness which lasted for around 10 min. Once the cloudiness was gone I did some tests and surprisingly the Alk was still at 7.1 dKH, Ca 400 ppm but, Mg dropped to 1460ppm.

Admittedly I don't have any chemical background but, I was expecting Alk and Ca to have dropped not, Mg dropping - probably my chemistry ignorance. I assume the precipitation was the magnesium...

So, I guess I just found the problem, dosing too much of Mg, Alk and Ca... Not sure if you agree?

Now, if you agree that I am correct, what would you recommend as the course of action in order to avoid messing the parameters further?

I had already stopped the Mg dosing (was dosing Mg Sulphate + Mg Chloride on a ratio of 1:7) via a dosing pump and now have reduced the CaRx output to 25ml/min...

In any case, if you could provide a bit of steer would be highly appreciated!

Many many thanks in advance!

Best,
Jose.