Cal-Mag in Coco...Yes or No

[2ShedsJackson]

New member and first post so here goes...

Just started on my 3rd indoor grow in 1m x 1m tent with Spiderfarmer SF2000 lcd lights. I had big problems with the first two grows, mainly bugs and diseases for the first one ( my fault ) and for whatever reason seemingly instant death just before harvest on the second ( probably my fault again ). For that reason I want to cover all bases with this latest effort.

Seedlings have just sprouted in small starter pots, 1 indy and 1 sativa, and I'm now prepping my 70/30 Coco/perlite in advance of transplanting to air pots. This time around I'm using rainwater only + nutes for the grow.
Because the rainwater only has very low TDA of 30-40 as opposed to 350 - 400 with tap water, i'm reading that I should incorporate Cal-Mag. I've settled on BioBizz for Cal-Mag and all the other nutes - Bio Gro, Bio Bloom & Top Max.

Am I doing the right thing with the Cal-Mag and should I add it at every watering.

TIA

[Ckbrew]

Yes, use calmag with every watering/feeding. Coco contains chelation sites that bind Ca+ and Mg+ which will make them unavailable to the plants, therefore it needs to have those sites saturated (buffered) with calmag. I use 10ml/gallon for the first soaking only, then 5ml/gallon for the first week, then 3ml/gallon for all feedings afterward right up to 1 week before harvest.

[Allotrope1000]

Hi, 2Sheds.
I grow in an outdoors greenhouse using 50/50 coco/perlite and always use CalMag. Ckbrew is spot on in his post. Cal (Ca2+) and Mag (Mg2+) are essential.
Magnesium is the central cation (positively charged ion) in the chlorophyll molecule (ligand), so the plants need a steady supply.
I suppose one can use hard tap water with a lot of calcium and Epsom salts for the magnesium, but why fuss with it? Simply follow adding GWE's recommended CalMag supplement to your nutrient soltion. Don't let not buying a $20 quart of CalMag cause you more grow problems. GWE pretty much gives you fool proof buds if you follow their advice.

[2ShedsJackson]

Thanks CkBrew & Allotrope1000 for your advice of adding to every watering which I'll now follow throughout the grow. I used tap water previously and as both of those grows ended in disaster I want to have total control over what I add to my plants for this one. I have very hard water where I live but have no idea what the concentration of, or indeed which minerals it contains.
I'm going to let both seedlings get their roots established in the small pots before I transplant to the air pots, so maybe another 3 or 4 days.
Annoyingly the SF2000 lights haven't turned up yet so I'm stuck with my old 'budget' Koscheal 1200w until they do.

[golfnrl]

You should be able to find a published report for your local water quality and what it contains. Have you measured the EC in your tap water before you add nutrients? EC is a measurement of the 'stuff' that is in your water, right? If you have hard water that's a good number to know. For me, the resting EC is .36. I deduct that from the total the meter reads to get the net number I am after. If collecting the rainwater is a hassle you can easily use tap water if you know the starting EC and correct the PH every time you water your plants.

[Bluey]

Do as CKBrew recommends but keep an eye on them for too much N going into flower. You may have to reduce or eliminate the calmag sup early in flower if your plant is on the too heavy N side as I typically have to in most of my grows. Calcium and magnesium are present as nitrates in most calmag suppliments

[Smallgrow]

I’m not the coco pro that the folks above are, but a reminder to wash and prep your coco properly before you start. If it’s not already done. Generally that includes some cal mag to pre buffer
Sounds like your heading in the right direction but here is a link to full coco info on the main site if you haven’t been there.