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I know a lot has been discussed recently in various forums about the relationship between Ca and K uptakes and their respective ratios. Is there any information about Ca and Mg? Or even about Ca, K and Mg together? Will excessive Ca competetively inhibit uptake of K and Mg?

My water is well water from N Florida. In composition, it would be similar to that which you would find in a spring. High in CaCO3. When it dries on glass or chrome, you see the white deposit ring of CaCO3. When you boil it, it comes out of solution. The KH is 9.5, GH is 12-13. Being so high in Ca, I wonder if it might inhibit Mg or K uptake by the plants?

The reason I ask is because I keep having this pesky problem with L. repens and a repens cross. They tend to develop holes in older leaves and periodically seem to undergo a period where the growing tip dies. It just turns black and it has to be pruned off. The plant does grow, but it seems to go through these 'phases'. This is supposedly one of the easier growing plants and able to withstand hard water, especially since you can find it growing in springs and rivers around here. The problem has occurred in all 3 tanks, which all have different substrates (flourite/eco/gravel-florite mix). Tanks are co2 injected, NO3/PO4 dosed 2x weekly, micros dosed on the other days.

I have started to add 1/2tsp of MgSO4 to my 29 gal and 1/4tsp to my 10 gals, but it's too early to tell any results. Should I add more Mg? I haven't added K2SO4 figuring, sufficient K was being added via the KNO3. 50% weekly water changes.

Sorry for the length, any comments/suggestions welcome.[/i]
 

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I have not had issues with high Ca/Mg and low/high K. However, I have had problems with LOW Ca/Mg and HIGH K, where certain plants (roots/stems/leaves/etc.) literally melted away w/i 24 hours. At the time, Hygrophila augustifolia/lacustris were the most severely affected, followed by Eusteralis stellata and Lobelia cardinalis 'Dwarf'. Myriophyllum matogrossense 'Green' was the least affected. Micranthemum umbrosum/micranthemoides, Blyxa japonica, and Rotala sp. did not exhibit any symptoms. I could induce other plants into the melting extravaganza by keep adding more KCl/K2SO4. When I upped [Ca/Mg], I can add more K w/o inducing melting. Now, I am not sure if this antagonistic behavior is between Ca & K or Mg & K or Ca/Mg & K. To further complicate matters, I am not sure if Cl had anything to do with it because at the time, I used both KCl (Muriate of Potash) and K2SO4. :oops:

I would be interested in hearing about other's experiences with these minerals.
 

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Bert, it's not the tap water.
Those plants grow all over the region there.
I've had them there also.

General Ca:Mg ratios are 4:1, does not matter too much as long as you have enough.

That whole thing with K+ inhibition and Ca++, is hogwash. I've been around on it and did the test myself, I did not find anything that could be Ca blockage, so did a few others at very high K+. Erik went up to 100ppm of K+ with Ammania, I went to 50-60ppm ranges. Neither of us found any blockage effects as claimed by several folks on this particular plant that was the one in question with many that reported the theory.

Make sure it's not shaded, add enough KNO3 and CO2.

Regards,
Tom Barr
 

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Perhaps it wasn't the inhibition of Ca by K or whatever other combinations of these nutrients, but can you comment on the melting phenomenon that I have experienced and why the addition of KCl/K2SO4 aggravated the problem? Was it coincidental and I simply missed some other variable?

What sort of overdose/deficiency/inhibition/etc. would cause aquatic plants to melt like that? Is there something similar in terrestrial plants or hydroponic cultures that we can look to for clues?

I am really curious. Thanks Tom.

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A search on the APD turned up a few melting reports but no conclusions were derived. As for the whole K/Ca debate on there, no consensus were achieved save for additional K supplementation is unnecessary if KNO3 is employed.

Perhaps after the AGA, I'll attempt to replicate the phenomenon. :mrgreen:
 

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I can tell you what it is NOT much easier.

Generally if adding something causes an issue, you likely are limited somewhere else, eg more K+ drives the NO3 uptake faster etc.

Regards,
Tom Barr
 
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