Low Calcium, and perhaps low Mg

[FireViper]

The calcium levels in our tank dropped over the last couple weeks, from around 450 to around 300 or so. So I did a little research and stumbled upon another thread where someone suggested that low Mg could be causing the low calcium. So I went out and picked up a Red Sea Mg test kit. Tough little syringe to get 1ml in, but figured it out.

Anyway, it appears our Mg is around 1280. According to some online sites, that's about normal for sea water. Perusing threads here, most suggest that Mg should be around 1350-1400 for a reef tank.

Assuming that I do indeed need to raise the Mg, I again assume gradually is the best bet. Picked up some Seachem Mg and some Seachem Calcium supplements. I guessing start with Mg first, then go with some Ca? Or should I do a little bit of both from the get go?

Thanks!

[reefnoob88]

How big is your tank, what do you have in it and how often do you do water changes?

[FireViper]

Originally Posted by reefnoob88

How big is your tank, what do you have in it and how often do you do water changes?

55 gallons. 10% water change every other week. Live sand, live rock, diy rock, a dozen or so small corals, 4 clowns, two gobies, and two firefish. Pics in another thread. The Calcium drop seemed to coincide with adding the diy rock. All other parameters are okay, with dKH of 8 (143ppm).

[FishAndPhysics]

Sorry, what do you mean by diy rock?

[FireViper]

Originally Posted by FishAndPhysics

Sorry, what do you mean by diy rock?

Do It Yourself. Mix of cement and live aragonite. Cured for two months until no change in pH.

[FishAndPhysics]

Have you tried adding a Ca additive? Would be interesting to know if you test your Ca, add Ca, test again, it you get the rise in Ca you should. It could be that something in your rock is causing Ca to precipitate out.

[FireViper]

Is a 1280 Mg too low? The other thread suggested that levels of Mg that are too low could cause low Ca levels. Should I add both Mg and Ca supplements?

[FireViper]

Tested the sea water I'm using from the LFS--Ca is around 350 to start with.

[reefnoob88]

350 Ca is a bit low for a reef tank you might wanna consider asking what salt they use but anyhow do you do any dosing?

[FireViper]

Originally Posted by reefnoob88

350 Ca is a bit low for a reef tank you might wanna consider asking what salt they use but anyhow do you do any dosing?

They use filtered sea water from the Pacific.

No clue as to dosing. Been doing this for a couple of months and this is the first time our parameters have been off.

[reefnoob88]

Originally Posted by FireViper

They use filtered sea water from the Pacific.

No clue as to dosing. Been doing this for a couple of months and this is the first time our parameters have been off.

The natural sea water is good but your corals are using up more Ca and Mg then your water changes are replacing. This is perfectly normal every reefer deals with this, some hand dose and some have an automated dosing systems. As your corals grow and get bigger they will use it up even faster and thats the struggle with keeping your parameters in line. So you can pick up some Ca and Mg additives there is tons to choose from or do more water changes as this will bring it up as well. I would strongly suggest watching some videos on youtube before you start adding anything to your tank though its not hard its just not something you wanna do blind. Im sure if you ask or search through this forum you will find someone who knows a whole lot more then me.

[Uncle99]

What's happening to ALK?

[FireViper]

Originally Posted by Uncle99

What's happening to ALK?

dKH of 8 (143ppm)

Thanks all for the help!

[outssider]

1280 for mag isn't really low. That's what the average ocean water is at. I would make an effort to not let it drop below 1200....shoot for 1280- 1400....

[FireViper]

Thanks for all the help!

[dkeller_nc]

By the way, you will have to start daily dosing alkalinity (sodium bicarbonate/carbonate) and calcium relatively soon - water changes will not be nearly enough to keep up. And from the standpoint of the health of your corals, it's important that the alkalinity not fluctuate more than 1 dKH or so in a 24 hour period.

So long as you're dosing small amounts of an alkalinity supplement (and a matching calcium supplement), you should stay within this range until your corals really start taking off, at which point you're likely to need a dosing system.

You'll also want to be thinking about getting a water purification system (RODI) so that you can make your own saltwater (as well as having water for top-offs). Natural seawater is a bit risky for a reef tank. For practicality's sake, it's collected fairly close to the shoreline, and the chemistry parameters will potentially fluctuate quite a bit depending on local rainfall and the resulting runoff.

Here's some reading to do about Reef aquarium water chemistry:

Reef Aquarium Chemistry (general)

Calcium and Alkalinity

Solving Calcium and Alkalinity Problems

[FireViper]

Originally Posted by dkeller_nc

By the way, you will have to start daily dosing alkalinity (sodium bicarbonate/carbonate) and calcium relatively soon - water changes will not be nearly enough to keep up. And from the standpoint of the health of your corals, it's important that the alkalinity not fluctuate more than 1 dKH or so in a 24 hour period.

So long as you're dosing small amounts of an alkalinity supplement (and a matching calcium supplement), you should stay within this range until your corals really start taking off, at which point you're likely to need a dosing system.

You'll also want to be thinking about getting a water purification system (RODI) so that you can make your own saltwater (as well as having water for top-offs). Natural seawater is a bit risky for a reef tank. For practicality's sake, it's collected fairly close to the shoreline, and the chemistry parameters will potentially fluctuate quite a bit depending on local rainfall and the resulting runoff.

Here's some reading to do about Reef aquarium water chemistry:

Reef Aquarium Chemistry (general)

Calcium and Alkalinity

Solving Calcium and Alkalinity Problems

Great suggestions. Thanks! Looking at RODI soon. Great point on the sea water. Though the LFS stuff comes from the ocean, my daughter did a science project where she needed some brackish water. Collected it from the northern San Francisco Bay (actually the San Pablo Bay for those keeping score). Came in at a surprising 1.005 salinity--barely qualified as brackish.

Learning and having fun! Addicting little hobby.