Dosing Mg and Ca?

reef_grrrl · Jan 3, 2016

I really just need someone to hold my hand for a minute here...

Hi guys, for our purposes my tank is about a year old (it has a four year back story but I re-did it last year with new rock and added a sump and fuge).

It's a 20 gallon system with a 5g sump, total water volume is 20 gallons, 5 gallon water change every 2 weeks with reef crystals.

I've been slowly adding more coral, and recently- past few months- have gotten brave and branched into SPS, so my tank currently has a bunch of softies, about 15-20 heads of frogspawn, 20+ heads of duncans, three decent sized plates, a chalice frag, some montipora, one tiny pocillopora frag, a hitchhiker sps?, and a ping pong ball sized frag of turbinara.

Everything seems to be growing moderately, though I don't have much to compare my growth to...

Up until now, the water changes have been keeping things fairly balanced with my few corals, but now consumption is up as my new frags grow... I noticed the biggest drop in alk, so I recently started adding kalk to my top off water.

Tonight, I tested my water and here are the applicable results..

Salinity 1.025
Mg 1050
Ca 400
Alk 9.8

So dosing! This will be my first time dosing anything besides adding the kalk to my ATO. I guess I need to be manually dosing Ca and Mg, so what are yalls favorite products?

njtiger aquariums · Jan 3, 2016

I use the Red Sea Reef Foundation product. I found it to be simple to use but have noticed that my corals eat the alk up quickly.

redfishbluefish · Jan 3, 2016

Your alk and calc numbers are fine. However, with Reef Crystals, I don't believe your MAG number. Can't be that low with RC. Have someone else test your MAG.

acesfull44 · Jan 3, 2016

redfishbluefish said:
Your alk and calc numbers are fine. However, with Reef Crystals, I don't believe your MAG number. Can't be that low with RC. Have someone else test your MAG.

I am not hear to hijack this thread, but I also use Reef Crystals, and have almost identical #'s, just tested again today!

njtiger aquariums · Jan 3, 2016

I use Reef Crystals and did a water change yesterday and tested today and here are my numbers:

Cal - 420
Alk - 8.1
Mag - 1480

reef_grrrl · Jan 3, 2016

redfishbluefish said:
Your alk and calc numbers are fine. However, with Reef Crystals, I don't believe your MAG number. Can't be that low with RC. Have someone else test your MAG.

I can retest tomorrow also, I thought it was a bit low, I don't know anyone else with a legit test kit, and I visit a LFS maybe once a month. I use the Red Sea pro kit, and it's been 2 weeks since my last water change if that makes any difference. Thank you!

redfishbluefish · Jan 3, 2016

Now it's been some time since I've used RC, but when I did, the MAG number was always in the 1400 range. Unless they have reformulated, that's what I'd expect.

Please review the test instructions. A common mistake with the Red Sea kit is not adding a total of 5 drops of Reagent A. I've seen where folks only add 1 drop, not seeing the x5 over instructions 2 and 3.

Downbeach · Jan 4, 2016

That does look like a testing error, or a bad kit. Here is a good demo, in case you haven't seen it:

A couple other things worth mentioning: before you start using a new container of salt it would be good practice to thoroughly mix the salt to ensure there hasn't been any elemental stratification during shipping. Next I would make sure I have an accurate SG(I prefer 1.026) measured using a properly calibrated device/meter, i.e. refractometer calibrated with a 35ppt solution(not RO/DI or distilled water). If you're using a swing arm type hydrometer, or a non/mis calibrated device can lead you, unknowingly, to add too much/little salt mix to your make up water, and by extension too much/little Ca, Mg and alk. I used RC for many years, and would get readings of: Ca @ 450ppm, Mg @ 1450ppm and Alk @ 13 dKH at a SG of 1.026(35ppt) in freshly made SW for WC's.

Waters · Jan 4, 2016

Reef Crystals does mix with low Mg.....I tested a while back since my DT was showing low but I can't remember exactly what the numbers were. I add a 1/2 cup of Kent Mg. to every new batch of Reef Crystals I mix up (in a Brute can).

Randy Holmes-Farley · Jan 4, 2016

I agree that most people who see low magnesium like this are experiencing magnesium testing error, which is VERY common.

There may be bad batches around, and there may be inhomogeneous buckets of salt that settled during shipping (so different levels of magnesium at the top and bottom, perhaps), but the forums are filled with impossible magnesium results that cannot be anything but testing error.

I would not rush to dose magnesium. It certainly didn't deplete in your tank to that level. Magnesium depletion is not going to be more than about 1/10th of the calcium depletion, so if calcium is not depleted, then magnesium will be reflecting what is in the salt mix (whatever that is, but for Reef Crystals and most mixes, it is an adequate amount; RC normally has more than enough magnesium).

I personally wouldn't even bother to chase this down, but if I were to, I'd get a confirmation on the magnesium levels using a different kit. Then act based on this further testing, if needed.

reef_grrrl · Jan 4, 2016

Wow you guys are so on point and so helpful!

The last water change was my first with a new bucket of RC, but I did roll it around throughly to mix it. I know I added 5 drops of reagent a, because my husband was making fun of how long it takes to swirl after each drop. I think what might have happened is an error with the titration syringe, I tested mg first, and was surprised when I filled the Ca titration syringe to see how much solution was in it, compared to the Mg, so I will pay closer attention tonight when I retest.

kevindo123 · Jan 4, 2016

I disagreed that RC have enough Magnesium. I put in BRS magnesium when I mix my salt to get it in the 1350+ range. I keep chalices so this level is required. The low magnesium can also cause calcification of the sandbed.

Randy Holmes-Farley · Jan 4, 2016

kevindo123 said:
I disagreed that RC have enough Magnesium. I put in BRS magnesium when I mix my salt to get it in the 1350+ range. I keep chalices so this level is required. The low magnesium can also cause calcification of the sandbed.

What salinity did you use and how did you measure it?

An off batch is possible, certainly, but the normal manufacturing specification for RC at 35 ppt is magnesium close to 1400 ppm, which is more than enough.

How do you know your kit was giving accurate results?

Randy Holmes-Farley · Jan 4, 2016

As an example of how I think "bad batches" are often test error, this is the sort of result that proves test kit error exists.

This person was testing many different kits on the same water and comparing them.

https://www.reef2reef.com/threads/t...rt-elos-redsea-hanna-etc.222909/#post-2568694

For magnesium, he got

1470-1480 (Salifert)
1100 (Red Sea "Curse it and crush it! We hates it forever!" Pro Mg)

So if he had only used the Red Sea, he'd say he got a bad batch. If he only used Salifert, he'd say he had way more than enough magnesium.

I'm not sure if either is correct, but definitely at least one is not.

njtiger aquariums · Jan 4, 2016

Randy Holmes-Farley said:
As an example of how I think "bad batches" are often test error, this is the sort of result that proves test kit error exists.

This person was testing many different kits on the same water and comparing them.

https://www.reef2reef.com/threads/t...rt-elos-redsea-hanna-etc.222909/#post-2568694

For magnesium, he got

1470-1480 (Salifert)
1100 (Red Sea "Curse it and crush it! We hates it forever!" Pro Mg)

So if he had only used the Red Sea, he'd say he got a bad batch. If he only used Salifert, he'd say he had way more than enough magnesium.

I'm not sure if either is correct, but definitely at least one is not.

I did a test like this as well. I tested API, Red Sea, and Salifert for 6 weeks. I did find the Red Sea and Salifert mags were off but seeing how I never had my water professional tested I don't know which one is correct. Now I use the Red Sea kit cause I dose Red Sea so figure I should follow their test results