Question of the Day Current thinking on the Ca:Mg:K ratio?

[Marwen]

That's probably about right on K, I've done K lower than Ca. There is not really a golden ratio, it will all depend on your tank. But starting K a bit higher than Ca seems to be the way to go.

Yes, even in crops and hydroponic nutrient solution science, there is no golden ratio because it's all dependent on the specific plant and pH, etc. What's "optimal" for tomato vs lettuce vs strawberry, etc. will all be different. And it's very safe to assume that the same will go for aquatic plants.

Having said that, say you want to make one general-purpose nutrient solution that you can use for growing different crops, then a a K:Ca ratio in the 1:1 to 2:1 range is considered good.

Ca:Mg would be about 2:1.

And then you have things like the Ca:B ratio, where a range between 160:1 and 400:1 would be good. So if boron is 0.05 ppm in a planted tank then Ca between 8 and 20 ppm would theoretically give the highest B availability. Doesn't mean that at 40 ppm Ca, you wouldn't have the same results especially at pH 6.5 or less. Because B would still be non-limiting at that level. (As long as it's kept at SAFE levels for bacteria/microorganisms and plants along with copper and zinc. Which BTW the toxicity threshold for beneficial nitrifying and algae-inhibiting microorganisms is lower than that of higher plants.)

@Marwen this is very well said. Would you say front loading is also something that these tanks do that plants get used to?

I would say so, yes. Almost all successful aquarists I've studied do it, even if not explicitly.

Surprisingly however, most commercial fertilizers that prescribe daily dosing don't mention this. With the exception of Marian's Masterline, the product instructions say to dose back about 2-3 daily doses after a water change (since that's what he does).
So if you take his "Boost" all-in-one formula (which I know he personally uses in his tanks), and you look at the total weekly dose, it's 10.5 ppm NO3. But when you count the front-load dose, it's actually 15 ppm NO3 per week. So about what @GreggZ doses if I remember correctly.

Personally since I DIY all my ferts, I treat macros/micros like my RO remineralizer:
- I have macros/micros bottles (non-chelated traces here) for daily dosing (currently waiting on an auto-doser so they'll be hooked to that).
- I have separate bottles for reconstituting the RO: even calcium is added in liquid form through CaCl and CaNO3 (since I don't want to deal with powders for more ease of use), magnesium, potassium, phosphate, iron and traces (traces I've chelated with DTPA here so they linger more in the water).

So remineralizing adds back not only the 12 ppm Ca and 5 ppm Mg, but also NPK+traces. And it's calculated for only the water change volume. That's my "front-loading" and it's the bulk of what the water contains at all times.

The daily dosing is just adding back what I've tested/estimated to be my average daily uptake. And it uses a little more bioavailable forms of nitrogen and iron (carbamide, and a tiny bit of NH4, tiny bit of Fe-gluconate along with the DTPA).

This leads to a pretty stable TDS from day 1 to day 7.

Would I obtain the same results from simply 1 front-loaded dose per week? Most probably. LOL
For example Marian does that, 1 dose a week in his big tanks. (Using his all-in-one Boost formula since it contains only NO3 nitrogen so safe to front-load, contrary to his Golden formula which has urea.) Couldn't get easier than that.

It's just that the lab sciency aspect is part of the fun for me personally is all.