Cal in soil? Tap water

Many of us are soil growers myself included, I personally run 2/3 ffof and 1/3 ffhp (mixed with Perlitre and mkyos).

Now unless your growing a photo monster ive read it’s near impossible to have a mag deficiency, if your growing in fresh soil.
So that aside I wanted a discussion on if we need cal to be added?
If your running tap water like myself you have minterals in your water Wich for me is mainly cal and mag.

My water sample is here:

Now personally I mostly run autos and use tap water so I’m wondering if I even need it, but again I would like to discuss at what point do we or don’t we if we at all need it in soil.

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I run distilled water so I’m going to have to add both at some point. I’m going to let the plant tell me when though.

Calcium deficient:


Mag deficient:


Your photo didn’t upload so I will add the mag images.

@FlxerPower have you grown start to finish with FFOF & RO water? Did you get noticeable deficiencies?

@Nicky I’m on my first growth in years. I don’t know what to expect in terms of timing to see a deficiency. I’m gonna guess that I’ll have to run more than one plant through the soil before I have to supplement. I’m using Dr. Earth Pot of Gold soil and I bet it’s loaded with nutes already. I’ll just keep some cal mag on hand for when it comes up.

Often you have to supplement, not because calcium or magnesium isn’t present but rather it’s in a form the plant can’t access. Nutrients are designed to be soluble in the range cannabis likes and sometimes you can have a lockout due to other elements interfering with uptake.


You run a load of soil through more than one grow?
I use fresh soil every time, because you have to flush after and by the end of veg most of the nutes have been eaten by the plant.
I Geuss if you have a live organic soil it might be differnt…

@Myfriendis410 hence the importance of humic acid and kelp in a 5:2 ratio… Hmm

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Adding to what Myfriendis410 started, I am almost certain lighting plays a huge role in various deficiencies including cal-mag. Worded differently lots of light causes heavier feeding.

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Over on AFN I was reading about people running into countless isuess on 24/0 light schedules and that’s why the majority run 20/4 and second most run 18/6 (I’m running 18/6 right now)
Also LED’s tend to cause more nute uptake on the cal/mag side then CMH

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Plants definitely need a rest. They grow in the dark too!

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Yeah well the auto genetics come from the north where daylight is 24hr on for the summer so many thought elswise.
I think most realize now that even autos need a bit of a rest.
Would like to see a control of 18/6 vs 20/4


Ha. No. I see mag def in almost every grow. I’m also in a blend of ffof and ffhf.


Absolutely, great point!

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Okay that’s good to know!
At what point do you start feeding cal/mag?

I haven’t had a calcium deficiency but like clockwork, mag deficiency around mid flower (also use ocean forest). I’ve seen it enough that I start adding epsom salt around week 3 flower.


Okay so that being said might as well start adding cal/ mag 2nd week of flower or so
Well there goes that plan lol

@Drinkslinger & @Bobbydigital

How do you feed while in ffof?
Do you wait until your run off TDS drops before you feed any nutes? I remember it starts out like 4000 TDS or so, historically I haven’t fed any nutes until the TDS dropped below what my scedule has said to depending on week.

So I read my TDS first and then once I drops below what chem gro sais it should be at I feed accordingly.

This is what I do

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I watch the runoff as well as the plant. If it needs something I add it. Otherwise I generally wait until the ppms drop to below the recommendation. That’s usually in month 2.


Just follow the recommended flushing interval FF publishes and monitor the TDS as you stated and you will know when it’s time to add nutes. Best to not add any but we’re in containers so (almost) no way around it.

Adding Epsom is a good dose of magnesium but not calcium. It does promote terpenes and flavinoids. Not a bad thing and I do it too.

In my first grow I was using distilled water and they got stunted because distilled water is not the correct PH balance for the plants. I then changed the water to tap and PH balanced the water between 5.5 and 6.5 and they continued to grow nicely.

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Yeah you have to PH your water sooooo important.

@Drinkslinger & @Bobbydigital
What feeding /TDS scedule do you follow?

@Myfriendis410 yeah I have dry analyzed cal and mag that also both came in 5lb bags lol.
I didn’t know fox farms has a flush scedule for soil I’ve never done it… Hmm

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