MG was used years ago, back when most still had the cave man thinking that assumed PO4 = algae.
Then it was NO3 = algae........
Then plants release allelopathic chemicals........
All these claims are easily falsified and have been many many times.
You add it to a reference aquarium by someone who has good control over their CO2, or stable CO2 in a non CO2 enriched tank.
Adding activated carbon (AC) removes all the allelopathic chemicals.
AC is what is used as a control. If the hypothesis is that alleopathic chemicals are preventing algae, then adding AC would induce algae blooms.
I have, and no one else has, to my or anyone's knowledge, ever even seem any correlation of any sort with AC and algae, if anything, less algae.
Plants and algae do not compete for nutrients, they are in such vastly different scales, different life histories, they are far far removed from the other. Light is about the only one I can think of where they really compete much.
Give this a read:
http://books.google.com/books?id=oD...#v=onepage&q=Nutrient uptake kinetics&f=false
Heavy read for most hobbyists, but gives a detailed account of the issues with uptake rates, competition between species and the large macro algae(which are much like FW plants) vs the smaller microphytic algae in terms of ecology and competition.
Old news really, but hobbyists rarely get this stuff, and why the fact of the matter is algae appears when you have poor nutrients for aquatic plants.
If all you are looking at are nutrients, like P, N, K, Ca, etc........then obviously that is all you will see and look for.
If you look at CO2 and the demands there, then you might have a better picture.
If you look at light+ CO2+ nutrients, now you are getting somewhere.
If you look for light+ CO2+ nutrients + easy management of these 3, time and stability, now you are starting to really put everything together.
Nutrients are pretty easy truth be told, getting the others all together is a quite another matter. The people factor is also very huge.
Folks do many things differently, have different goals and expectations.
So the much of the issue are folks not having the light/CO2 correct.
Then they blame nutrients.
Without having the light/CO2 independent, you cannot say much about nutrients, or algae. Many try.:silly:
That said, small amounts of MG can work, but NH4 is a bit like playing with fire.
NO3 from KNO3 is pretty safe.
NH4 locked in sediment is fairly safe.
Since it only takes a small error, MG is not that suitable.
MG is also not that cheap..........look at KNO3, KH2PO4, etc, I pay about 2-3$ a pound.
MG is 6-10$, maybe less on sale etc, but it's not that large of difference, it's more a convenience factor.
www.aquariumfertilizer.com
Regards,
Tom Barr