Mg deficiency in flower

So I am about 3 to 5 weeks from harvest and I am developing a Mg deficiency. I was wondering your opinions on if I should give some calmag this close to harvest and if i should go with the 5ml/g dose. Thanks in advance.

Epsom salts can treat a magnesium deficiency, plenty good to use where you’re at too.


Can you post a few pics in natural light?

Cal mag typically has nitrogen, which you don’t want in late flower. Earth juice makes a cal mag product with no N, it’s called “oilycann”.
If it’s just magnesium then Epsom salts, as dbrn32 suggested, is an inexpensive and readily available solution.


I dont have any in natural light at the moment, they are sleeping. I can post some this evening, after 5 if needed.

It’s in one plant more than the others and just a small portion of the leaves starting with the older lower growth. It has just now, yesterday started reaching the higher leaves and a second plant has started showing slight signs.

How much should I add to 1 gallon of water?

I dont know if you can see it or not but there are also some red/purple stems of the fan leaves.

Also, just some other info, run off is 6.5, ppm around 2500 after feed, the in between without nutes waterings it drops down to around 1000. Watering with 6.5ph. Checked soil ph, it is also 6.5. So I dont think it’s a lockout situation.

One last detail lol, I have softened city water so i think that is where my definitely is coming from. I’m using ff trio.

Are you softening the city water where you live, or is the city using softeners? What’s the ppm of the water at the tap?

Have you been following fox farms flush schedule?

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I’m curious too. Those kinda look under fed in general.

GOSH, this looks like my issue.

I would suspect a potassium deficiency but need to see in natural light. This would cause calcium and magnesium deficiencies to show up. You are also a long way from harvest based on the flower pics you put up: a month?

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Yes, about a month away

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I soften it with an on demand softener because otherwise it leaves calcium deposits all over everything. The ppm from tap is about 300-400.

Do you have a faucet that doesn’t put out softened water? Sometime a hose or washing machine spigot?

I believe so. I can bypass the softener with a valve though.

Softening water adds salt. Salt buildup in cannabis medium is not good. Do you happen to know the ppms of your water before it’s softened? You might be better off using it.

Have you been following the fox farms flush schedule?

Might be a lockout from salt build up.

I do not. I can bypass the softener and find out though. I have flushed to schedule although I only started adding nutes in the first week of flower because I had them in ffof. I only flushed with water, not the sledgehammer. I am gonna go and get some distilled and stop using the faucet from now on. If I were to flush with some r.o. or distilled that should help with any salt buildup, no?