Why is my Mg always so low?

c_scherer123 · #1 01-20-2010, 02:02 PM

I have had my 20g for about 8-9 months. I have perpetually low Mg, even though I dose it bi-weekly or more often. The fresh salt batches come in at 1400 mg.
Calcium is 500
Magnesium is 900

I can tell when my magnesium is below 1200, as all my polyps (especially the GSP) and torch corals close up.
I did notice that the coraline algae is starting to grow all over the rocks and glass. I removed the small bit of chaeto I had and that noticeably helped keep the MG level steadier.

Any ideas?

fishytime · #2 01-20-2010, 02:07 PM

whats your DKH at?.....those three (Ca, Mg and DKH) need to be balanced....my guess is your having trouble raising it because of an imbalance in your other parameters.....

The Grizz · #3 01-20-2010, 03:06 PM

My Mg is low as well but my Ca is a 480 and DKH is at 8.5. Tested Mg last night and it was 1150.

Jason McK · #4 01-20-2010, 03:50 PM

Are you sure when you first mix the SW for a water change it's at 1400? What salt are you using

c_scherer123 · #5 01-20-2010, 04:19 PM

I will check DKH and salt names when I get home.
Last time I checked, the DKH was fairly high (unusually so), but so it is also high in my fresh salt mix.

Delphinus · #6 01-20-2010, 05:24 PM

Dumb question but I'll ask it anyhow .. when you're dosing Mg, are you dosing it to bring it back to 1400 or are you dosing the amounts suggested on the bottle? Oh wait, IS there a bottle? What are you dosing for Mg?

Here's my take. Mg is an underappreciated element by the powers that be within the hobby. Commercially available Mg to dose is like taking a peashooter to a shootout where the other gunslingers are carrying Uzi's (Ok my metaphor sucks, but I'm too lazy to think of something else. I use the "it's like draining a lake with an eyedropper" metaphor far too often and it's time to shake things up a bit). I would buy a $30 bottle of Mg solution from the LFS and then end up dumping the entire bottle into my water change water to make it 1400. So now I just buy 20-30 lbs. of MgCl crystals from LittleSilverMax because it's a far more cost effective solution, costs me maybe $80 or whatever but I end up with enough to fill a 5g salt bucket which lasts 6 to 12 months. I end up adding 225ml of it (almost a full cup) to my makeup water to make 1400 and when I dose my tanks I found it surprising how much of it I would need to raise Mg by 100. I forget how much exactly (I write stuff like that down so that I don't need to remember it, consequently, I don't remember what it is when I'm writing a post like this. Sorry.

)

So if you're using a commercially available product to dose Mg and just following the instructions of "one capful per X gallons", my bet is that this is just not enough to maintain Mg. It wasn't for me anyhow and I'd be surprised if that truly works for anyone.

Over time Mg will deplete just like Ca and Alk will. Think I've heard the addage that the depletion rate is roughly the same per week as it is for Ca or Alk per day.

c_scherer123 · #7 01-20-2010, 05:52 PM

Quote:

Originally Posted by Delphinus

Dumb question but I'll ask it anyhow .. when you're dosing Mg, are you dosing it to bring it back to 1400 or are you dosing the amounts suggested on the bottle? Oh wait, IS there a bottle? What are you dosing for Mg?

Here's my take. Mg is an underappreciated element by the powers that be within the hobby. Commercially available Mg to dose is like taking a peashooter to a shootout where the other gunslingers are carrying Uzi's (Ok my metaphor sucks, but I'm too lazy to think of something else. I use the "it's like draining a lake with an eyedropper" metaphor far too often and it's time to shake things up a bit). I would buy a $30 bottle of Mg solution from the LFS and then end up dumping the entire bottle into my water change water to make it 1400. So now I just buy 20-30 lbs. of MgCl crystals from LittleSilverMax because it's a far more cost effective solution, costs me maybe $80 or whatever but I end up with enough to fill a 5g salt bucket which lasts 6 to 12 months. I end up adding 225ml of it (almost a full cup) to my makeup water to make 1400 and when I dose my tanks I found it surprising how much of it I would need to raise Mg by 100. I forget how much exactly (I write stuff like that down so that I don't need to remember it, consequently, I don't remember what it is when I'm writing a post like this. Sorry.

)

So if you're using a commercially available product to dose Mg and just following the instructions of "one capful per X gallons", my bet is that this is just not enough to maintain Mg. It wasn't for me anyhow and I'd be surprised if that truly works for anyone.

Over time Mg will deplete just like Ca and Alk will. Think I've heard the addage that the depletion rate is roughly the same per week as it is for Ca or Alk per day.

I first bought the liquid stuff, but I found it pretty useless, so I am now using crystals http://www.petsandponds.com/en/aquar...p17157180.html. I didn't find out about Littlesilvermax until after I bought the big container. I dose a max of 1 tbsp per day to avoid shocking my corals (who told me they disapprove of larger MG swings). I generally dose 2-4 days per week.

fishytime · #8 01-20-2010, 06:33 PM

Try using this http://www.reeftime.com/reef-chemistry-calculator.asp ....it will tell you what you need to dose of each chemical to get your parameters balanced

kien · #9 01-20-2010, 06:48 PM

Your Calcium is 1500ppm ?? Wow, I have never seen anyone run calcium that high. Is that just how it comes out in your Salt Water mixes or do you dose to get your Calcium to that level?

Delphinus · #10 01-20-2010, 07:52 PM

Oooh ... good catch Kien. Calcium can't be 1500 that sounds way too high. I thought you meant 500 which is still quite high but not impossibly so. As for adjusting Mg you should be able to adjust by 100 per day, when I target Mg in my tanks I'll go whatever amount gets me a 100-150 rise in Mg and then just repeat that daily until I've hit 1400.