After dealing with moderately soft water, and now hard water I have noticed a similarity in the doseing solution required for better plant growth.

With both water sources I have used the ratios of NPK suggested in EI scaled back for my low light application. Soft water growth problems were relatively easy to solve by doseing Ca and Mg with each waterchange.

But here in Orem Utah, the water is quite hard and I had issues with getting good growth again. With more than the recomended K doseing for even high fish load systems I still had deficiency symptoms. Even when I got that to go away (I doubled the K) I still didn't have very good growth. Only after adding plenty Mg have I gotten reasonable growth.



I know for systems with CO2 added there is a minimal gh requirement generally supplied by adding a CaMg mix both to keep the ph stable and to supply the plants with those nutrients.

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If your tap has high Ca is there a minimum Mg and K level needed for the plants to be able to access those nutrients? What would that ratio look like?

If x Ca in tap then z K and y Mg nessasary for good plant growth.


Given that EI addresses the NPK ratio, could the relationship between Ca Mg and K explain why some tap sources grow plants more easily than others?

EI doesn't address any ratio at all. It merely recommends a dosing schedule that maintains adequate levels of the needed nutrients. Ratios of nutrients have not been shown to be significant for plant growth.

GH has no effect on pH, with or without CO2. KH, which in ideal water is carbonates, does affect pH.

Plants do need some magnesium, so if your water is virtually magnesium free you should add some magnesium as a nutrient.

No, I guess EI is not really based on a ratio so it doesn't matter if you dose 10-10-10 ppm NPK. It could be pointed out that that would be way more P than is needed implying that there is some sort of aproximate ratio after all.


Your saying that there arn't ratios got me to thinking about what the ratios are in my tank and I understand now that I had deficiency inhibition not Ca inhibition.


I get a some N from the fish food, so I do need more K... it just doesn't make sence how much more though. I dose K like it is used more than any of the others, and if I back off I get holes in the older leaves.



I ran my cheap tests on my tap water. I don't fully understand the results, the tank gives evidence that Mg is rather low, ie growth slows unless I dose enough to bring levels up to a minimum 2 ppm



40-60 ppm Ca++ probably 40-50 as it almost changed at 40

120-140 ppm Gh

100-110 ppm Kh

This is Utah with a lake giveing evidence to the presence of other salts in the water, but it seems odd that that much is not Ca or Mg.

I guess my question really is about how much Ca is inhibiting and at what point is that a concern.


I read a chart that said that high levels of Ca, Mg or K would inhibit the other two, but it didn't give any indication as to what those levels might be.

i havehad anywhere from 50-60 ppm of Mg here in Davis, 90 ppm Ca++ etc, and up to 200 Ca++ elsewhere.

Never seen any issues related to inhibitions.

You will need more traces or switch to TMG with harder tap.
That's about all.

Regards,
Tom Barr