Magnesium and calcium

[Zero Nitrates]

I have a 400 gallon system with no coral, three tangs, some snails, macro algae and some mangrove. No coralline algae.

The system is using up 400 ml of magnesium and 200ml of calcium per week. Alk is stable at 8.5.

What is using up the calcium and magnesium?

 

[chrisparks]

Any live rock or just base rock? What kind of salt are you using?

 

[Zero Nitrates]

200 lbs of live rock
Instant ocean
no water changes during the period I tested

 

[chrisparks]

Man that is alot of calcium but I have never had a tank over 120 gallons. I know live rock will use some but not that much. When was your last water change? When I had my 120 it seemed like if I went over 5 weeks without a water change I would have to dose more to keep my calcium up until I got around to a water change.

 

[Randy Holmes-Farley Verified Community Expert]

I have a 400 gallon system with no coral, three tangs, some snails, macro algae and some mangrove. No coralline algae.

The system is using up 400 ml of magnesium and 200ml of calcium per week. Alk is stable at 8.5.

What is using up the calcium and magnesium?

Test error, or water changes with a salt mix lower than your tank. Nothing is using noticeable amounts of magnesium in your tank, and nothing uses either of those without also using alkalinity. A drop of 1-2 ppm magnesium and 18-20 ppm in calcium requires a drop of about 2.8 dKH in alkalinity when it is being precipitated or consumed.

 

[Zero Nitrates]

I use the test kit on two other systems with no noticeable discrepancies. Although that is a possibility. It is the Red Sea kit.

I haven't done a water change on the system since it was set up in January.

I was wondering if the mangrove and cheto could be using the calcium and magnesium.

 

[Randy Holmes-Farley Verified Community Expert]

I use the test kit on two other systems with no noticeable discrepancies. Although that is a possibility. It is the Red Sea kit.

I haven't done a water change on the system since it was set up in January.

I was wondering if the mangrove and cheto could be using the calcium and magnesium.

Not enough for rapid changes. Many people have problems with the Red Sea magnesium kit.

 

[Zero Nitrates]

What test kits do you use?

 

[Randy Holmes-Farley Verified Community Expert]

Me? I didn't test often. I went mostly by the look of the tank, after keeping it for 20 years.

I used a pH meter for pH, and DIY titration for alkalinity. I never bought one, but I'd use the Hanna ultra low range for phosphate. I used manty kits over the years, and generally like the Salifert kits for calcium, magnesium, and alk.