High Cal Low Alk Low Mag

[D. Torres]

Had my LFS test my water. I’m not sure how accurate this fancy tester is but they swear by it. Based on their test I need to make some adjustments. I tested myself with API test for everything except for magnesium and phosphate I used a Salifert test kits. My numbers were as follow

Alk 7 dKh
pH 8
phos 0 or undetectable
Cal 450
Mag 1095
Nitrate 10

I know my Mag is low but my concern is my Alkalinity. Based on their test that number converts to a 6.2dKh. I’ve never dosed but I have the Red Sea Foundations ABC (calcium, alk, mag). My question is from what I am reading is that I’m supposed to dose Calcium and Alk together but if my Calcium is already where it should be or slightly higher can I just dose Alk? For reference I have a 20g AIO with mostly softies. Have a couple smaller acan colonies an open brain coral, a dozen BTAs(they’re a pest honestly) a clam and some zoa frags. Any advice would be greatly appreciated. Thank you.

 

[Randy Holmes-Farley]

My concern is the accuracy of the magnesium testing. Magnesium that low is more likely to be test error than real. I wouldn't raise it based on that test (even with both tests). It is not easy to get magnesium that low, and in your case, seems quite unlikely.

What salt mix are you using and what do you think the salinity is?

The Red Sea product is not made for 1:1 dosing. If you did dose both parts of a balanced 1:1 two part, the calcium rises would be very small for the alk you need and I'd recommend it. The calcium rise would be too small to reliably detect if you added 1 dKH of alk with a balanced additive.

In this case, I'd just add the alk part as needed.

 

[D. Torres]

My concern is the accuracy of the magnesium testing. Magnesium that low is more likely to be test error than real. I wouldn't raise it based on that test (even with both tests). It is not easy to get magnesium that low, and in your case, seems quite unlikely.

What salt mix are you using and what do you think the salinity is?

The Red Sea product is not made for 1:1 dosing. If you did dose both parts of a balanced 1:1 two part, the calcium rises would be very small for the alk you need and I'd recommend it. The calcium rise would be too small to reliably detect if you added 1 dKH of alk with a balanced additive.

In this case, I'd just add the alk part as needed.

My salinity is 1.025. I have an ATO on that system so it is relatively stable. I do 5 gallon weekly water changes which is another reason I don’t understand why both the my Alk and Mag are low. I thought I would get enough replenishment from my water changes.

 

[Randy Holmes-Farley]

How are you measuring salinity?

 

[D. Torres]

How are you measuring salinity?

With a refractometer calibrated with BRS refracto juice.

 

[Randy Holmes-Farley]

Weekly water changes do little for alk when there is any significant demand, but the magnesium will only be that low if it is test error, or the salt you are using is low in magnesium (or salinity is lower than you think). Which mix?

At a sg of 1.025, magnesium will be lower than normal (compared to 35 ppt, sg = 1.0264, at a sg of 1.025, the natural level of magnesium (1280 ppm) drops to 1212 ppm.