I think
this comment by
@X3NiTH provides a helpful insight to the Ca:Mg ratio discussion.
Totally. It illustrates what plant tissue requires - we need not provide anything out of what is needed. It is almost the meta of Leidbig, a lens into a potential true "ceiling".
But we are allowed ... and if we do, the plant may be able to move that where it is needed. For example, suppose that PO4 is needed in the leaf and it is absent of the column ... but it is present at the root ... well let's go ahead and transport it. Conversely, suppose that PO4 is needed for root developement but your substrate is inert ... load the column with PO4 and have the leaves move it down: do this on start up and voilla rapid root growth ... hurrying your establishment. Remember, you force feed phosphate via the plant leaf pathways I linked in my first post. Force feed phosphate ... through the column ... drive demand of all nutrients ... BOOM super fast establishment -- provided everything is provided.
EDIT: Try this with Potassium and what happens? Nothing. Why are ADA plants smaller than EI plants (despite feeding EI levels of K --- yet their growth rates are nearly identical: substrate tops off the rest)? Because the plant can moderate potassium - but potassium is essential in activating photosynthesis ... specifically in enzymatic activity. We cannot withold it - that's why even in low GH, most people dose at least 15 K ... but some don't ... and those that don't it is ok! Because the plant tops itself off from substrate OR we simply reduce the demand by ensuring that potassium is not the limiting nutrient ... make it nitrogen -- and this isn't coincidence -- Amino acids are the structural building blocks of all protein ... despite Phosphate driving ATP ... we need proteins first to build the organelles. As such, limit N and voilla you can keep K above the Leidbig ceiling. But you can MORE easily induce deficiency in this way -- forget to feed your fish and you can induce algae if your substrate runs out -- why? Because if you overfeed you drive demand via N availability. Simple. So you are on a tight rope between feeding and not feeding. But can potassium affect nutrient acquisition? Certainly, it is a positively charged species and as such repels other postive stuff and attracts negative stuff (organics)... the more stuff the more tug o war ... but perhaps the plant can accomodate ... of course it can ... by polarizing leaf, using pathways, growing a certain way ... blah blah blah ... take all these things and this is why twisting is associated with "potassium deficiency" ... unless it is topped up from substrate .... aha this is the crux of why "some people say excess works or it doesn't" -- Think I went on a rant. Sorry about that! But let's keep going ... Given a plant species, there will be a unique value (relative to ALL parameters in question) such that the effects of Coulomb is "masked" and can be misinterpreted as "just leidbig driving everything". Try it. Pull a nutrient from your dosing and watch the tank crash ... each plant crashes at different rates. -- The easiest is to just stop turning on CO2 for two days, you can immediately see which ones demand more CO2 than the others (whether that is free CO2 in the column OR the pH that facilitates CO2 acquisition) ... THIS will be different based on your KH. BUT this won't be true if you use low light ... it will take you two weeks to notice anything -- compound this with low temperatuer and it may take even longer (WHY - it requires longer to use up the stores from your previous feeding) ---- NOTE: My "days" 2 days and 2 weeks are approximates and completely meaningless. Last one: So why advocate for higher values of light, because the system as a whole benefits more ... but this is ALSO dependent on our goals as a fishkeeper; so at times, low light is suitable and other times high light is.
But what happens when hobbyist attempt to grow plants under .3 Ca and .1 Mg in the column with inert substrate.
Or 300 Ca and 100 Mg ... with inert substrate.
Both cases, it isn't going to work
well.
Why? Because there is an assumption that what you put in the water actually makes it into the plant. And this assumption is the crux of the argument between common ideologies of the hobby. This is why we cannot quote Leidbig in the absence of Coulomb and we cannot quote Coulomb in the absence of Leidbig. And if we think on this, we will realize something (and I will come out and say it):
1) EI = Leidbig
2) Anti-EI = Coulomb
We've missed it. Coulomb facilitates acquisition. Leidbig dictates acquisition.
Moreover, if you throw an active substrate into the mix, then perhaps the plant can top up any short comings and grow ... for the first few months and then the tank crashes. This is a regularly reported phenomena by people in the hobby and often they throw out substrate and start again ... but why then can people grow in inert (here's the crux ... they do 3x weekly water change and load up to perfect targets by percent each time ... this will obviously work and it can be illustrated by this framework --- suppose on the other hand that you have far too many species in that same tank ... then it will fail - UNLESS you pick plants appropriately to grow together).
Josh
EDIT: Need to add that substrate masks our inadequacies to providing optimal water conditions catered to each species and it's unique ability to acquire nutrients. It masks the effects of Coulomn, since it provides a bank of nutrients for the plant to access at all times --- but we can't assume it's free -- if the nutrients aren't within a range of acquisition for roots, then it won't work. Now OF COURSE the plant can adapt how it acquires nutrients from its roots and THIS will very likely influence the microbiology that grow around the root facilitating nutrient motion into plant tissue -- it's absolutely remarkable -- this is equivalent to different plant forms under different water column conditions that facilitate nutrient acquisition and CO2 acquisition at leaf (and generally shoot tissue) interface.
