Water hardness question

[Decisive]

I just got a TDS meter and tested my tapwater, it reads 300ppm. If I switch immediately to RO water, will the excess calcium and magnesium in my soil from having such hard water be offset. That is will i see any benefit to switching from tapwater to RO water from now to the end of my grow. I am currently at the end of my second week of flowering and have 6 weeks to go before i finish, before this i vegged for 2 weeks from rooted clone, so they have received tap water for a total of 4 weeks now. Thanks in advance.

 

[Weedninja]

Yes. The plants will consume the minerals already in the soil. Is your pH ok? Next time around, try a mix of 50/50 tap to RO. That will take your TDS to around 150-175 ppm, which is excellent.

 

[habeeb]

are you doing organics?
do you have lime in the soil?

no offset, the plant will just need cal / mag most likely down the road. your decision to make, as most say 300 is the cutoff for PPM.

 

[Decisive]

thanks for the replies guys, my pH going in is 6.5 adjusted on both nutrients and water. My soil mix is a 1/3rd each of perlite, vermiculite and peat moss all with no nutrients in them to begin with. I didnt add lime to my soil mix this time.

 

[Blue Dot]

thanks for the replies guys, my pH going in is 6.5 adjusted on both nutrients and water. My soil mix is a 1/3rd each of perlite, vermiculite and peat moss all with no nutrients in them to begin with. I didnt add lime to my soil mix this time.

You did add lime you just didn't know it. Hard water is soluable lime, ca and mg carbonate.

The finer the lime, the faster it is broken down. Your lime in your hard water is pretty fine but will still take up to 6 months to break down. Some will break down in the interim, just not all at once.

When you say you pH adjust your tap water if you adust it by using phosphoric acid the P will combine with the Ca to form calcium phosphate. This is harder to break down then calcium carbonate so that ties up a bit of the ca for a while.
(Ca carbonate is what sea shells are made up of and bone is made up of ca phosphate. Both are broken down by acid.)

You just added lime to your soil everytime you watered and not ahead of time like most growers so if you watered enough then you limed enough and the pH should be stable.

What does it matter anyway, a fert like GH floranova will have plenty of Ca and mg in it so you won't have to worry how much you have in your soil.

I mean you're not planning on watering with just straight RO water are you? That would be silly.

Lime is added more for pH correction then it is to supply Ca and Mg.

 

[Decisive]

You did add lime you just didn't know it. Hard water is soluable lime, ca and mg carbonate.

The finer the lime, the faster it is broken down. Your lime in your hard water is pretty fine but will still take up to 6 months to break down. Some will break down in the interim, just not all at once.

When you say you pH adjust your tap water if you adust it by using phosphoric acid the P will combine with the Ca to form calcium phosphate. This is harder to break down then calcium carbonate so that ties up a bit of the ca for a while.
(Ca carbonate is what sea shells are made up of and bone is made up of ca phosphate. Both are broken down by acid.)

You just added lime to your soil everytime you watered and not ahead of time like most growers so if you watered enough then you limed enough and the pH should be stable.

What does it matter anyway, a fert like GH floranova will have plenty of Ca and mg in it so you won't have to worry how much you have in your soil.

I mean you're not planning on watering with just straight RO water are you? That would be silly.

Lime is added more for pH correction then it is to supply Ca and Mg.

thanks for the explanation, what is your best recommendation going on from this point? Simply continuing ignoring the carbonate/phosphate buildup while adding a cal-mag plus (fox farm nutrients have no cal/mag in them) to ensure usable ca/mg levels? or to start doing as weedninja suggested i.e 50% RO/50% tap to get a balanced ppm (i couldnt tell if you were being sarcastic).

 

[Blue Dot]

act as if nothing has happened. fert with whatever fert you're planning on using and mix this fert with ro water only. It will be the most stable that way and have the most proper npk. The little bit of lime present in your soil won't really make that much of a difference because the nute pH will overpower it fairly quickly.

mixing nutes into hard water never turns out well imo.

 

[Blue Dot]

thanks for the explanation, what is your best recommendation going on from this point? Simply continuing ignoring the carbonate/phosphate buildup while adding a cal-mag plus (fox farm nutrients have no cal/mag in them) to ensure usable ca/mg levels?

Yes, mix your fox farm into ro and ADD calmag. The ca in calmag is in the calcium nitrate form and is 100% immediately soluable/miscible/useable. The ca carbonate in your soil is not immediately soluable so forget about it. You still may have to pH adust your nute mix because I've heard FF can be low pH.