Is the calcium in tap water available to plants?

beta · Nov 14, 2018

I feel like I'm running a slight Ca deficiency, but by the numbers my tap water (~0.4EC) has enough in it to not need a supplement. However I recently ran across the info that most of the Ca in tap is in the form of Calcium Carbonate, which isn't very soluble. Does that mean most of the Ca in tap water isn't available for the plant to uptake? If so, that would explain my slight def.

fwiw I use Jack's Hydro @ 3.7g/gal and Calnit @ 2.5g/gal in tap water. According to info I've gathered elsewhere that works out to 152-51-211-125-62-80 (N-P-K-CA-MG-S) in RO (in other words, not counting the tap water).

Thanks!

beta · Nov 14, 2018

Followup: Would top-dressed agricultural gypsum (Calcium Sulfate Dihydrate) make for a good Ca supplement in my coco / DTW system?

ReikoX · Nov 14, 2018

beta said:
Followup: Would top-dressed agricultural gypsum (Calcium Sulfate Dihydrate) make for a good Ca supplement in my coco / DTW system?

Garden gypsum is water soluble. Add about 1/4 teaspoon per gallon and water into the soil.

Snook · Apr 29, 2021

beta said:
I feel like I'm running a slight Ca deficiency, but by the numbers my tap water (~0.4EC) has enough in it to not need a supplement. However I recently ran across the info that most of the Ca in tap is in the form of Calcium Carbonate, which isn't very soluble. Does that mean most of the Ca in tap water isn't available for the plant to uptake? If so, that would explain my slight def.

fwiw I use Jack's Hydro @ 3.7g/gal and Calnit @ 2.5g/gal in tap water. According to info I've gathered elsewhere that works out to 152-51-211-125-62-80 (N-P-K-CA-MG-S) in RO (in other words, not counting the tap water).

Thanks!

This thread is a few years old, thanks Beta, but never really answered the OPs question. Is the calcium in tap water available to the plants?
if tap is 160ppms (dont know the composition of it) and I'm targeting 600ppms in RO (10-20PPMS) should I calculate the 160ppms into the 'formula'
and make it 760ppms? or 160ppm tap + 440ppms nutes to go to 600ppms? 160 ppm tap too much?

f-e · Apr 29, 2021

If you measure 0.4 at the tap, then perhaps 60-80ppms of that is elemental calcium, which is what we use in our count. It was fairly soluble as it left the ground and came out your tap. It's mostly in a carbonite form though. Your use of pH down plays a role here. Using Nitric on a hard water supply might convert half of that to calcium nitrate which is as good as it gets. I just made this thread myself and put up better details. You need to know how much nitric you usually use, to add it first. Then it has the best chance of burning off the carbonites. Phosphoric acid is quite different. It will form an insoluble precipitant with the calcium carbonite, so it's lost not improved. The other route is chelates such as humic which will both carry the calcium and protect it from the acids. I use nitric then mop up with humic.

Snook · Apr 29, 2021

f-e said:
If you measure 0.4 at the tap, then perhaps 60-80ppms of that is elemental calcium, which is what we use in our count. It was fairly soluble as it left the ground and came out your tap. It's mostly in a carbonite form though. Your use of pH down plays a role here. Using Nitric on a hard water supply might convert half of that to calcium nitrate which is as good as it gets. I just made this thread myself and put up better details. You need to know how much nitric you usually use, to add it first. Then it has the best chance of burning off the carbonites. Phosphoric acid is quite different. It will form an insoluble precipitant with the calcium carbonite, so it's lost not improved. The other route is chelates such as humic which will both carry the calcium and protect it from the acids. I use nitric then mop up with humic.

Thank you f-e for your response... I wish I knew what all that means exactly.. I run ppks with ro and jacks+ca @ 600ppms.. the simplicity, to me, is in many years not worrying or adjusting PH.
Whatever PH is at 600ppms is what it stays at thru-out the run. I dont know how the tap water (160ppms) is going to affect change to the 600ppms/PH levels with the tap water. I'd really like to ditch the RO but am not willing to go with tap instead of RO in the mix without some direction. The tap water affect in Veg is one thing, bloom is another.

f-e · Apr 29, 2021

When we measure the tap water, there is a lot more being measured than elemental calcium. The ratio's of all the stuff measured depends on the water source. A typical 0.4ec supply as wanted by most feeds, gives 60-80ppm of calcium. It can be wildly different, but we don't see problem posts very often. When we do it's usually the use of RO because the water was well above 0.4ec.

If you measure 160ppm at your tap, that is quite clean. Unfortunately I can't convert your ppm measurement to ec, and ec is the only thing we can measure, and as such, the only thing we can talk about reasonably. I will hazard a guess that you can just think of it as RO water, and have your end mix 160ppm higher. It's likely just Ca in there that could have any real effect. Maybe 40ppm but I don't know as you don't have an EC meter. Is your Calcium additive just Calcium or is it Calcium Nitrate. Using less Calnit to account for the taps Ca would lower Nitrogen. That could have greater consequences.

Your local lab will test a sample of tap water for irrigation suitability. Telling you what's in it. Bill has a long thread running about cheap nutrient lines that revolves around Jacks. Many speak it's hard and soft water variants, used with hard and soft water. Often using the standard soft water version with hard water to gain more Ca. The substrate is of great importance though. In soil you might have so much Ca that a bit here in there is meaningless. While in coco you must reach Ca targets. Add LED lighting, and like me, you could end up chucking the dummy if you don't meet Ca demands in coco.

Snook · Apr 29, 2021

f-e said:
When we measure the tap water, there is a lot more being measured than elemental calcium. The ratio's of all the stuff measured depends on the water source. A typical 0.4ec supply as wanted by most feeds, gives 60-80ppm of calcium. It can be wildly different, but we don't see problem posts very often. When we do it's usually the use of RO because the water was well above 0.4ec.

If you measure 160ppm at your tap, that is quite clean. Unfortunately I can't convert your ppm measurement to ec, and ec is the only thing we can measure, and as such, the only thing we can talk about reasonably. I will hazard a guess that you can just think of it as RO water, and have your end mix 160ppm higher. It's likely just Ca in there that could have any real effect. Maybe 40ppm but I don't know as you don't have an EC meter. Is your Calcium additive just Calcium or is it Calcium Nitrate. Using less Calnit to account for the taps Ca would lower Nitrogen. That could have greater consequences.

Your local lab will test a sample of tap water for irrigation suitability. Telling you what's in it. Bill has a long thread running about cheap nutrient lines that revolves around Jacks. Many speak it's hard and soft water variants, used with hard and soft water. Often using the standard soft water version with hard water to gain more Ca. The substrate is of great importance though. In soil you might have so much Ca that a bit here in there is meaningless. While in coco you must reach Ca targets. Add LED lighting, and like me, you could end up chucking the dummy if you don't meet Ca demands in coco.

Thank you for you guidance and thoughts f-e. :good:

. EC meter? Truncheon... EC, 160 ppms = .2ish EC.. but yes, adjust the CA down a point and go with 760 PPMs (1.5 EC).
One other thing I have a hard time wrapping my head around is.. buffering... RO = no buffering (I think) tap water, I've read and maybe my interpretation is wrong , adds some buffering that will/might affect PH. Yeah? Nay?

f-e · Apr 29, 2021

RO has nothing in it. So a tiny drip of something pH 5 and the whole barrel is pH 5. There is nothing in there to counteract the pH change or modify whatever was dripped it. The pH 5 stuff will just disperse through the tank. Presuming it's soluble.

The above is a bit black and white. There is always a little grey, like the RO not really being perfectly clean.

Tap water has stuff in it. Keeping things black and white, it could be 160ppm of stuff, so just a small amount (lets say10ppm) of your pH 5 is no longer so dominant. The tap has some resistance to change.

That's the slightly confusing buffering. Like a railway buffer resists the train, the crap in the water resists change. Some crap offers more resistance than other crap.

If your tap is 0.2 than backing off 0.1 will probably more than compensate. Half the tap isn't calcium. However, I don't know that your bottle of calcium is all calcium either. While I'm chucking a few numbers around here, It's just calculator stuff and not real world experience. I can't get you any closer to the same mix. The variables... lack of experience... I just don't really know.

I do like how RO makes pH almost academic. You can spend all day adjusting it, but ultimately the substrate and plant will have more effect than anything we do. I have found it's usually pH up I want with RO and it just makes the plants unhappy if I try. My tank can sit at pH 4.2 and still run from rockwool at pH7. It offers very little buffering until you start loading up with calcium and the like.

Snook · Apr 30, 2021

f-e said:
RO has nothing in it. So a tiny drip of something pH 5 and the whole barrel is pH 5. There is nothing in there to counteract the pH change or modify whatever was dripped it. The pH 5 stuff will just disperse through the tank. Presuming it's soluble.

The above is a bit black and white. There is always a little grey, like the RO not really being perfectly clean.

Tap water has stuff in it. Keeping things black and white, it could be 160ppm of stuff, so just a small amount (lets say10ppm) of your pH 5 is no longer so dominant. The tap has some resistance to change.

That's the slightly confusing buffering. Like a railway buffer resists the train, the crap in the water resists change. Some crap offers more resistance than other crap.

If your tap is 0.2 than backing off 0.1 will probably more than compensate. Half the tap isn't calcium. However, I don't know that your bottle of calcium is all calcium either. While I'm chucking a few numbers around here, It's just calculator stuff and not real world experience. I can't get you any closer to the same mix. The variables... lack of experience... I just don't really know.

I do like how RO makes pH almost academic. You can spend all day adjusting it, but ultimately the substrate and plant will have more effect than anything we do. I have found it's usually pH up I want with RO and it just makes the plants unhappy if I try. My tank can sit at pH 4.2 and still run from rockwool at pH7. It offers very little buffering until you start loading up with calcium and the like.

My calcium is calcium nitrate from Peters. So back to experimentation to revile the facts.
Mixed up 5 gallons of nutes...> 5 gallons of tap (160 ppms/PH 9.1) and jacks pro + calcium nitrate (600 ppms) for a 760ppm mix and PH of 6.6.
The same mix with RO (15ppms/PH7.1) at 600 ppms/4.8PH. In the ppk, PH at 4.8 initially has been no problem with growth/yield/health of plant, so I'm
hesitant to run with the higher PH. I'll try the tap/nute mix (760/6.6) on rooted clones for validation.. Have also thought about 1/2 RO and 1/2 tap, in theory cutting the tap water PPMs to around 80 and lowering initial PH from 9.1 to something more reasonable and ultimately: 1. reducing the amount of RO needed by half and 2. lowering the initial tap waters ppms & ph by ??? some.

f-e · Apr 30, 2021

I feel the same trepidation thinking about a move from tap to RO. My tap is 0.3 while yours 0.2 and anything up to 0.4 shouldn't really be a problem. You think you may get a problem, while I have one I'm trying to pinpoint. Ultimately it's going to be a lot better if we can use the tap instead of a machine. Many people with high EC tap will use RO them put some tap back to see something like 0.2 so they are in effect jumping through hoops to get your tap water. They would love to be either of us. Though just an EC reading isn't knowing what is actually in there.

I'm getting some assistance from a lab friend. I don't really want to rely on guesswork or my water companies poor reporting. Time is money and a couple of hours head scratching could be turned into the cost of an irrigation suitability test. Which would be fucking awesome.

The use of nitric as pH down would help the tap calcium availability. While adding N. Doing that could allow you to lower your calnit use, as you are making your own.
An alternative is Phosphoric acid down, which lowers the tap calcium's availability. So keeps your mix really quite unaffected. Though you are making calcium phosphate which will precipitate. Most growers use tap and Phosphoric and the precipitate never comes up in conversation. I just don't like the idea as I reuse coco, which is going to act like a filter bag and catch it.

Snook · Apr 30, 2021

f-e said:
I feel the same trepidation thinking about a move from tap to RO. My tap is 0.3 while yours 0.2 and anything up to 0.4 shouldn't really be a problem. You think you may get a problem, while I have one I'm trying to pinpoint. Ultimately it's going to be a lot better if we can use the tap instead of a machine. Many people with high EC tap will use RO them put some tap back to see something like 0.2 so they are in effect jumping through hoops to get your tap water. They would love to be either of us. Though just an EC reading isn't knowing what is actually in there.

I'm getting some assistance from a lab friend. I don't really want to rely on guesswork or my water companies poor reporting. Time is money and a couple of hours head scratching could be turned into the cost of an irrigation suitability test. Which would be fucking awesome.
The use of nitric as pH down would help the tap calcium availability. While adding N. Doing that could allow you to lower your calnit use, as you are making your own.
An alternative is Phosphoric acid down, which lowers the tap calcium's availability. So keeps your mix really quite unaffected. Though you are making calcium phosphate which will precipitate. Most growers use tap and Phosphoric and the precipitate never comes up in conversation. I just don't like the idea as I reuse coco, which is going to act like a filter bag and catch it.

Yes, I remember wishing for lower tap EC but bought an RO filter, hence the want to switch back to tap. I may just start buying RO at the local RO machine @ $1.50/5gallons. The though has crossed my mind to use half RO and half tap (I think I've said this before). Dont know of a lab to test tap to individual parts. And although I want to 'believe' you're correct, I cant just jump in now at the last month or so of bloom. Starting next run with this mix might work but PH down is something I've used in the past that resulted in a complete drain down, flush and recharge of the whole system. Starting a run with this might result in the same but I'm thinking the effort might be worth it. I do have 2 plants in early veg, Zamaldelica boy about a month from seed and a Kali Mist (Km3) that is a twin to another KM3 clone. I've let them dry out some and watered with the tap/nute mix.. if there is anything bad about it I should see anything negative in the next day or two.

Guest · Apr 30, 2021

Snook said:
This thread is a few years old, thanks Beta, but never really answered the OPs question. Is the calcium in tap water available to the plants?
if tap is 160ppms (dont know the composition of it) and I'm targeting 600ppms in RO (10-20PPMS) should I calculate the 160ppms into the 'formula'
and make it 760ppms? or 160ppm tap + 440ppms nutes to go to 600ppms? 160 ppm tap too much?

Hardness is listed in calcium carbonate, about 25% of calcium carbonate is available calcium once decarbed

f-e · Apr 30, 2021

It's likely the calcium they measure, then list as carbonate. It could actually be in other forms. It's just conventional to list as a carbonate equivalent. The same as in feeds where we get calcium oxide numbers when it's not calcium oxide. I made the mistake of buying calcium oxide before finding its not soluble at anywhere near the levels we require. I could actually dissolve a tiny bit then get a drinking water report that told me it was carbonate. This is why an irrigation water report might be preferable. I'm not sure where you could live that stopped you getting one. It would be nice to see a sample report first though, to be sure of what was on offer. Usually there is an explanation sheet and recommendations.

Perhaps I'm being generous thinking 160ppm tap holds 40ppm of calcium. I'm just looking at the EC of 0.2 as being a third lower than mine. Which I calculated as 60ppm working backwards from the drinking water report offered by my (and almost every) water company.

Creeperpark · May 2, 2021

No calcium in tap water is not available to plants.

Tomatoesonly · May 16, 2023

Creeperpark said:
No calcium in tap water is not available to plants.

If it's not available, then why do nutrient companies make hard water specific formulas that don't have much if any calcium in them?

acespicoli · May 16, 2023

the stuff that falls from the sky is the only water you need

Dr.Mantis · May 16, 2023

Tomatoesonly said:
If it's not available, then why do nutrient companies make hard water specific formulas that don't have much if any calcium in them?

My guess is the pH adjustment most formulas include would render non-available tap water calcium as available. Most tap water Ca is in the form of carbonate or bicarbonate, if you drop the pH a good percentage will become available.

Ca++ · May 16, 2023

I use nitric, as it burns off the carbon, that leaves as dioxide. While bonding with the Calcium to form calnit. Plants will actively take N, with the Ca along for the ride.

Dr.Mantis · May 17, 2023

Ca++ said:
I use nitric, as it burns off the carbon, that leaves as dioxide. While bonding with the Calcium to form calnit. Plants will actively take N, with the Ca along for the ride.

Yeah, I really liked nitric acid when I used plain tap water. The other nice thing too, is all metal nitrates have very good solubility, so it can be very useful for flushing overly mineralized soils.

This time around, I’ve switched to citric acid as my pH corrector. Has nice chelating capabilities, and buffering capacity. Also, I wanted to see if there was any benefit to growing plants without any added nitrates. Time will tell!

Is the calcium in tap water available to plants?

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