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What do you prefer to use to supplement magnesium in your ap system? Just looking around for a quick fix until I can get something more long term established...

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Epsom salt (MgSO4-7H2O) has a 9.9 percent magnesium content.

or...

Magnesium chloride (MgCl2-6H20) has about a 28% magnesium content (if I recall). So use about one third the amount... 

Or if you need to buffer up your pH anyways...you can go with Dolomitic lime...which is about half calcium carbonate and half magnesium carbonate...

Don't over do it.. fish cant handle too much change in salinity all at once.

I think the bag recommends 1 cup per 100 sft of grows space. add about 1/2 of what you think you need then the rest the next day.

FTR - I add  3cups to 240sft of media and 2 cups in the 288sft rafts (FT and rafts = 2500 gallons total volume).

I have been using the cheap Iron test.. its now easy to keep it around 2.0

I usually add the Biomin Liquid Iron at the same time as the Mg  

Can I really just add epsom salt just based on the square footage of grow space? Don't I need some kind of volume or a ppm in there somewhere?

My salinity needs to be adjusted as well, so it would seem that epsom salt might be the way to go for me in a two-birds-with one-stone sort of way...Can I use that for both purposes? Adjusting salinity while supplementing magnesium?

I don't know of a mag test other than sending water samples to the university.

my understanding is that ..you really cant add too much, the plants will only take up what they need.. but if the salinity changes too fast, it could kill fish,

you will get a feel for how often your system need Mg in time.. as the plants go will from green to striped to green again..

its best to stay on top of it... when you first start to notice the yellowing, add it.  .. if you wait it could be uncorrectable.. with leafy greens.. it makes them hard to sell.

as for salinity,, Mg will change it too, but it takes a lot ..and remember to go slow.. over a few days.

you will need a hydrometer to check salt levels. there was a post by a former member (Rupert of Oz) that covered this very subject, rates and all ,,, but they are no longer viewable

the fastest way to treat a Mg deficiency is foliar spraying... its very water soluble, and works fast. and wont effect your salinity.use a wetting agent.

Thanks Rob! I ordered a salinity refractometer yesterday. If that doesn't work for me, I'll pick up a hydrometer. And it's good to know I can apply magnesium as a foliar spray; that's really helpful information.

While web surfing, I occasionally run into a mentioned concern of sulfate buildup in a system with the use of epsom salt...any thoughts?


Rob Nash said:

I don't know of a mag test other than sending water samples to the university.

my understanding is that ..you really cant add too much, the plants will only take up what they need.. but if the salinity changes too fast, it could kill fish,

you will get a feel for how often your system need Mg in time.. as the plants go will from green to striped to green again..

its best to stay on top of it... when you first start to notice the yellowing, add it.  .. if you wait it could be uncorrectable.. with leafy greens.. it makes them hard to sell.

as for salinity,, Mg will change it too, but it takes a lot ..and remember to go slow.. over a few days.

you will need a hydrometer to check salt levels. there was a post by a former member (Rupert of Oz) that covered this very subject, rates and all ,,, but they are no longer viewable

the fastest way to treat a Mg deficiency is foliar spraying... its very water soluble, and works fast. and wont effect your salinity.use a wetting agent.

I'd love to use dolomitic lime. Unfortunately, I battle with high pH during the winter since our well water is very alkaline... (is dolomitic lime and dolomite one and the same, or is there a slight variation?)

I'm still mulling over the idea of the possible use of worm castings as a "cure all" for nutrient deficiencies...Not that I mind adding supplements from time to time, and obviously it wouldn't be as simple as wormcastings+aquaponics= carefree days and prosperity for life, but if I can incorporate one thing and fix or prevent a multitude of problems, then that would seem like a good step.

Do you know of any natural sources of magnesium that could, say, be found in my backyard or in my house that I could incorporate into a compost? I kept running into coffee grounds as one potentially good source.

Vlad Jovanovic said:

Epsom salt (MgSO4-7H2O) has a 9.9 percent magnesium content.

or...

Magnesium chloride (MgCl2-6H20) has about a 28% magnesium content (if I recall). So use about one third the amount... 

Or if you need to buffer up your pH anyways...you can go with Dolomitic lime...which is about half calcium carbonate and half magnesium carbonate...

Hey Alex, it's really doubtful that you would even get within light years of any salinity issues if you went about this in even a remotely appropriate manner. So like Rob says, don't over do it! Now, I'm not much of a fish guy, but I've shocked the hell out of some fish parasites by rapid changes in salinity (from almost zero to 4-5ppt differences) and the fish do just fine, so I'm having a hard time imagining the almost industrial quantities of Epsom salt you'd have to add to accomplish such a goof up...(You'd almost have to be trying really, really hard to fuck up on purpose)

Calculating this sort of thing by using square footage of grow space is a pretty poor way to go about this sort of thing, unless were talking about a soil garden. Percentage in solution is what you'd be after here. Shoot for an addition that results in a  15-30 ppm change. I think there is a ton of threads in the search field on how to go about that, but if you can't find any for some reason, just ask before you start adding anything and we'll go over it again here. 

You can buy a magnesium test at any half way decent pet shop they are used for testing salt water.

Rob Nash said:

I don't know of a mag test other than sending water samples to the university.

my understanding is that ..you really cant add too much, the plants will only take up what they need.. but if the salinity changes too fast, it could kill fish,

you will get a feel for how often your system need Mg in time.. as the plants go will from green to striped to green again..

its best to stay on top of it... when you first start to notice the yellowing, add it.  .. if you wait it could be uncorrectable.. with leafy greens.. it makes them hard to sell.

as for salinity,, Mg will change it too, but it takes a lot ..and remember to go slow.. over a few days.

you will need a hydrometer to check salt levels. there was a post by a former member (Rupert of Oz) that covered this very subject, rates and all ,,, but they are no longer viewable

the fastest way to treat a Mg deficiency is foliar spraying... its very water soluble, and works fast. and wont effect your salinity.use a wetting agent.

Will a saltwater test work for freshwater? Sometimes you cant use the two interchangeably...

Steve R said:

You can buy a magnesium test at any half way decent pet shop they are used for testing salt water.

Rob Nash said:

I don't know of a mag test other than sending water samples to the university.

my understanding is that ..you really cant add too much, the plants will only take up what they need.. but if the salinity changes too fast, it could kill fish,

you will get a feel for how often your system need Mg in time.. as the plants go will from green to striped to green again..

its best to stay on top of it... when you first start to notice the yellowing, add it.  .. if you wait it could be uncorrectable.. with leafy greens.. it makes them hard to sell.

as for salinity,, Mg will change it too, but it takes a lot ..and remember to go slow.. over a few days.

you will need a hydrometer to check salt levels. there was a post by a former member (Rupert of Oz) that covered this very subject, rates and all ,,, but they are no longer viewable

the fastest way to treat a Mg deficiency is foliar spraying... its very water soluble, and works fast. and wont effect your salinity.use a wetting agent.

Yes i use them to maintain my calcium magnesium and alkalinity in my cherry shrimp and crystal shrimp tanks my ap system and my reef tank :) Never had an issue. I personally really like salaferts kits for mag http://www.petsolutions.com/images/Products/14013042.jpg  its available in most salt water fish stores.

Sweet!  im on it!   ..would have done that long ago, had I known.  after a quick google I see a zinc and copper tests, this might help shed some light on the heating element / zinc toxicity question.  I will report results asap. 

If im correct., were looking for a Mg level of 25-75 ppm

I am currently working on a master chem model of a health AP system and i came up with basically the same number you did tho it could be a tad higher with out any negative effects as long as your salinity wasn't above 2ppt.  I could be wrong I'm not finished yet so don't hold me to it but its where I'm at with that at the moment. Id fair to say that if your not keeping inverts its going to be hard to get just mag to be below its critical level in fresh water but its possible at this point in my life I'v seen almost every chem isolated and depleted by some source or another so nothing surprises me any more.

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