magnesium in sps tanks

[LawAce16]

Ok, I apologize if this is a settled area and the question is stupid.

I have been dosing B-Ionic for the last couple of years and it has just occured to me that my tank does not seem to have the amount of corraline algae that characterizes well established reef systems.

All my SPS are doing well (good color and growing, though slowy).

My tank's a 50 gal and I'm dosing about 1.5 cupfulls (dosing cup that comes w/B-Ionic) per day. I was wondering if the lack of coralline could be b/c of a lack of magnesium in the system. I have never dosed Magnesium, but do 10 gal water change/week.

I just thought I remembered reading something about Magnesium affecting the saturation point of calcium or something like that.

 

[Wiskey]

I use instant ocean salt, which is a little low in mag to start with. I dose Kent Tech M (mag supplement) to keep it at 1250, some people reccomend 1300.

Weither your lack of coraline algae is related to MG, I don't know, but it is used in skeliton building, and is used up in SPS tanks, so I would bet that it is worth checking.

I reccomend buying a salifert mag test and checking your tank, it is the only way to know for sure.

HTH,
Whiskey

 

[Wiskey]

Wow, I just realised I mis-spelled about every other word in that post!! That is a new record even for me.

Sorry,
Whiskey

 

[jsweir]

I am suffering the same symtoms as you but my Mg is fine. I think it is due to a lack of Strontium myself. I have a test kit and additive coming in today, so I'll find out for sure. JBNY posted pictures 2 months apart when he started dosing Sr and it was amazing how much corralline kicked in...

 

[DrBDC]

With regular water changes strontium should be close to NSW anyway. Mag would def. have a limiting effect on calcification as well as a harder time at keeping Ca and alk levels stable.

 

[jdieck]

Do you test your Calcium and Alkalinity? What are your normal levels?

 

[LawAce16]

My thinking is along the lines of what DrBDC said. I could be wrong, but I feel that 10 gal changes/week in a roughly 65 gal system is a substantial amount of water to be changing. At some point, it would seem to make sense that everything that can be accomplished with dosing supplements can be accomplished via water changes.

I know that water changes cannot suffice as a means of replenishing Ca because of the rate at which an SPS tank uses it (unless you do daily water changes). But, it seems like people do not dose every possible trace element in NSW, which means that people rely on most trace elements being replenished through water changes.

The question I guess gets framed in the following manner: Is Magnesium more like Ca or more like Iron (per se)? Can it be replenished through weekly water changes or does it have to be dosed as Calcium does?

 

[tgfrench]

up the alk level to around 12 dkh

 

[DrBDC]

Kind of half way between the two I guess. You can somewhat keep up but not quite so mag dosing is required but maybe with a weekly or every two week check. Some salts are higher than NSW in mag and with those it may be possible.

 

[LawAce16]

I think your analysis is spot on. For the past 2 yrs about 99% of my water changes have been done w/NSW from a LFS.

I've heard mixed things about using NSW from LFSs in the past and I think that this confirms it. I think that there are too many variables that cannot be controlled w/NSW bought at these places--dont know how long its sat in the container, phosphates, etc.

I've also heard a sleu of things about what salt is the best to use--what's everyone's opinion here.

 

[jdieck]

I could understand just depending on water changes for things we can not test but IMO for Magnesium, Calcium and Alkalinity nothing beats testing and add if required.