How much Cal-Mag for coco grow with hard water?

[Tone3000]

My water is truly hard: 400 ppm TDS without any additives. I am growing in a premixed coco-perlite blend, which contributes no nutrients. Too much cal-mag and I'll get lockout. Too little and I'll get deficiencies.

Should I start with 1 ml/litre and see what happens?

I would rather prevent the issues in the first place but I've seen recommendations to skip cal-mag when water is hard. However, that applies to soil grows. It seems coco coir always needs cal-mag? Or does it?

I am using the General Hydroponics nutrient trio for the grow (in addition to the cal-mag!).

[Tone3000]

Two days and no response...

This will be me second grow. The first one was watered with tap water that had been through the softener first (then nutes added and pH'd). It developed terrible deficiencies. Maybe if your water isn't as hard as mine to start, so you don't have a problem with too much salt in it after it's softened. I am on city water, not well water, so all of the hardness comes from Calcium (mostly) and Mag (some), and whatever else gets in there from dissolved limestone. I know a lot of folks are on well water, which gets hard too.

Maybe someone who has much experience growing in coco can chime in? What should I do about cal-mag supplementation?
Skip it until I notice a problem?
Start low and adjust if required?

Any advice from someone with more experience would be great!

[Mr.furley]

Short answer would be skip it.

400ppm is high for city water and if it already come with cal +mag+??? You shouldn't need it. Let your water breath over night to off gas anything from the treatment plant used to sterilize your water (chlorine-bromine-bleach) as it can also kills your microbi life fresh from the tap.

I have city water @250 ppms/ .4 EC and only use calmag to buffer my coco when I rehydrate it

[Tone3000]

Cute gif, LOL! Thanks for sharing your experience. If you aren't getting deficiencies, then that tells me I'll probably be OK skipping it. I'll give the coco (which I bought in a big bag, already mixed with perlite and ready to go) a quick soaking with a full dose of cal-mag (in water, then pH it) before I start.

[Ckbrew]

If your city water is that hard, I would start with getting a water quality report from the water supplier (they should provide this free of charge) and see what exactly is dissolved in the water. That will tell you Ca and Mg levels you are starting with. Then you can make a more informed decision about using a Calmag supplement. In general coco needs to be supplemented, but you need to know what you are working with from the start. If you are going to use the softened water, and it causes problems get that tested. You will have to pay for that one.

[Tone3000]

I had to email the utility to get detailed water reports. The one online was very basic. I was able to get the TDS from them as ranging from 430-450 ppm, which tracks fairly well with my readings of 400-430. The report Calcium around 65 ppm. Magnesium was not tested. There's also 35 ppm of sodium to start, without the softener. The rest of the things that are tested for are contaminants that are present in only trace amounts. There really isn't any account for what the rest of the dissolved solids are.

I can't say that this provides a whole lot of insight for me but maybe it means more to someone else! I have no idea how much calcium or magnesium, in ppm, my supplement actually provides or my plants would like. Is this info available someplace? It seems to be getting a bit deep into the nitty-gritty, though. I just want to make my plant happy!

[UndergroundFarmer]

Using a softener on water already getting a bit high in sodium is a bad idea! I think the limit is 50 ppm. I use my city's tap water which is usually 200-240 ppm from the tap. It delivers plenty of minerals from the limestone in the Missouri river's bed. You may want to look into a reverse-osmosis system. You could dilute your tap water with the RO water at about a 50/50 ratio to cut down the hardness and still get enough calcium and magnesium (and iron and copper and zinc and so on).

[Tone3000]

Hi Underground Farmer,

Thanks for your input! Are you saying that my raw, unsoftened hose water is too hard and it should be diluted with RO water? I was wondering if I could skip Cal-Mag supplementation in my coco grow since it is already 430 ppm TDS, 35 of which is sodium and 65 is calcium. Most sources (incl GWE) say that coco MUST have cal-mag added but I am getting the impression that my water will provide enough. Even when I was using the softened water, with all nutes added, it was 1100 ppm and I think I saw that the upper limit is 1500. Is that right?

I have a water softener on my tap water and used it on my first grow. Got an ok yield but lots of deficiencies, probably nutrient lockout from the high TDS in the water. I'm going to lug in hose water from outside from now on.

[UndergroundFarmer]

I've done DWC hydro, coco with bottle nutes and living soil with my tap water and haven't had calcium or magnesium deficiencies. If I was having to use your tap water, I'd lay off the Cal-Mag entirely unless the plants suffered. 1100 ppm is roughly 2.2 EC which is the strength I give for plants in their 3rd & 4th week of flower. Any other point in the grow I'd have it around 800 ppm or 1.6 EC or lower. I would definitely be sure to water to generous runoff with water that hard too. I understand not wanting to lay out $$$ for a RO system and then have to maintain it and deal with the low output vs the tap. It was a bridge too far for me back in hydro days.

I think skipping the RO for now and trying the unsoftened water should work. You can also dilute the hose water with bottled way cheaper and for nearly the same benefit if doesn't work out. Good luck!!

[Tone3000]

Like you, 1100 ppm was the highest TDS reading throughout the gow, the rest of the time it was lower also like yours, so hopefully it will be ok. You're right, I don't want extra hassle with RO water.

General Hydroponics makes FloraMicro for Hardwater but it's only available in gallons or larger. I am using the GH Flora trio now and the litres will probably last me 5 years. The gallon is $40 and I have been pondering whether or not I should get it.

Has anyone tried GH FloraMicro for Hardwater?

Did it seem to make a difference?