water Bioavailability of Calcium/Magnesium in hard tap water

[Zezryn]

Hey All,

I'm planning to cut my tap water with distilled water to lower the TDS for my DWC (5 gal) buckets. I realize this isn't optimal and I'm certainly aware of the pH and nutrient experimentation on my part to find the golden ratio for feeding. What I'm interested in knowing is if the Cal/Mag in my hard water is bioavailable to the plants so that I do not have to concern myself with adding liquid Cal/Mag during feeding. I've seen the posts all over the place about the molecular size of tap water Cal/Mag as being too big. I'd like to understand this better and would really appreciate an explanation or a link to an explanation in greater detail. I emailed General Hydroponics a week ago and here's their reply... [welcome your comments]

Good morning- the information regarding calcium in solution in your source water not being bioavailable is not accurate, anything that is detectable as TDS is going to be available to plants.


FloraMicro Hardwater formula is also discontinued, but was never meant to be a patch for poor water quality, it merely has half the calcium at 2.5% than standard FloraMicro at 5%.

This would compensate for calcium levels in source water around 75 mg/L, but above this- reverse osmosis filtration should be employed.


Take a look at our articles section to learn much more about water quality:


https://generalhydroponics.com/articles/


Thank you

 

[Gambleu]

Dissolved calcium and magnesium will always be in the form of Ca(or Mg)2+ ions no matter what source they come from. Problem is that many calcium and magnesium salts are poorly soluble and will readily precipitate out of solution, wich will obviously render them completely unavailable. Excess can also prevent other nutrients from being available to the plant, like iron.

 

[Zezryn]

Dissolved calcium and magnesium will always be in the form of Ca(or Mg)2+ ions no matter what source they come from. Problem is that many calcium and magnesium salts are poorly soluble and will readily precipitate out of solution, wich will obviously render them completely unavailable. Excess can also prevent other nutrients from being available to the plant, like iron.

Thank you.

If I'm understanding this correctly, the possibility of plants being able to pull these salts out of tap water for use is likely inhibited at best and fully unavailable at worst.

It stands to reason that the nutrient manufacturers know best how to suspend these elements in their products so plants find it readily accessible. I imagine the best way, as a grower, would be to know what to look for, as deficiencies, and adjust as needed. I can stomach the cost of a Cal-Mag solution, just think I might be able to get away with a minor dosing every so often. Is that approach sound?

I'd love to be able to crank out gallons of distilled water with my home unit (and use it exclusively) but at 5 hours per gallon, I'm shooting for 4 gallons a week for my DWC setup. I still have to create drinking water for the family too.

 

[Gambleu]

Well although my chemistry is excellent, i'm still new and learning in the hydroponic field and i don't know what's in your water so i can't really tell you what would work or not.

What i CAN tell you is that calcium in hardwater and calcium in calmag is the exact same thing, the thing is that calcium is never alone (its chemically impossible) and what commes with it won't be the same in tapwater or calmag. Like i sais before, calcium in too high concentration will react with many things, wich will completely mess your nutrient solution.

That is why many nutrient formulations comes in the form of A + B to be mixted in water and you have to add calmag to the other, the high concentration of calcium in A would form insoluble salts with B and screw everything, an effect that doesn't appear once they are sufficiently diluted.

What i can also tell you is that pH will be your most important parameter, as it directly affects what is available to your plant or not and what precipitates or not. If your water is very hard your pH is also likely too high.

Last thing, hardwater is perfectly fine to drink, the problem with it is scale formation and decreased soap efficiency. Unless there are other things you need to get rid off in your water i see absolutely no point in distilling it for your consommation, in fact minerals present in water are essential for proper hydration. Distilled water will be much easyer on your appliances, but not on your guts.

 

[Zezryn]

Thanks Gambleu. I appreciate your breakdown of the chemistry. Below is the 2020 water report for Lakewood, California. I'm beginning to understand that the other elements in my tap water, and their ratios, are important to understanding the way the Ca (and Mg) behave in solution. Supposing these elements precipitate out would agitation via stirring cause them to dissolve again? And could this be a remedy to the precipitation process and a stop gap measure for the plants having something to gather, albeit in a limited time frame? It certainly sounds like this may be an uphill battle but until I can crank out more distilled or RO water I'm looking for the workarounds.

I tested the pH of my tap water and it indeed did start out at 7.8 (below) but as I stirred and waited and re-rested, it made its way down to 7.3. It initially started out at 69 degrees F and with me holding the glass and waiting about 10 minutes or so, it managed to go up to 72 degrees F.

Anything down below that looks troublesome?

 

[Gambleu]

Supposing these elements precipitate out would agitation via stirring cause them to dissolve again?

Short answer : no stirring won't help. In the case of Ca/Mg, heating wil do even worse (that being said simply boiling water could be a simple way of softening your water if counter ion is carbonate, at the expense of a scaled boiler. If its something else it won't help)

As for pH, wait a few minutes until your reading is stabilised an take that number, many electrode (especially cheap one) will derivate when kept too long in your solution. pH IS temperature dependant, but many pH meter will compensate for temperature so this is normally not a problem. Reference pH scale is 77° F and pH goes down with higher temps. Regardless, 7.3 is still too high for pepper in hydroponic.

 

[Zezryn]

I'll focus my efforts on keeping the pH at 5.5-6.0 range and see where it takes me. I'll likely begin with a light feed of nutrients and scale up if necessary. I'll do my nutrient work per General Hydroponics light feed schedule as if I were dealing with full RO or full distilled water, realizing that my EC levels will be high but not necessarily as high as an aggressive feed schedule EC level. I will post pics and see how things go. Thanks for your help. Just waiting for my seeds to germinate.