About water and PH

Hello everyone.

As Im growing my plants in greenhouse, I cant take measurements from runoff so I dont know whats my soils ph, how should i do it?

Another thing, im watering my plants with river water and my ph meter shows that it has 8.3ph which is too high, what should i do? Add lemon Juice untill ph meter shows 6.5ph? What should i do as i have found that my plant is giving Cal/Mag Def and now grow is stunned. Take a look at pictures, what Made me think plant is having cal/Mag Def is that it got small Brown spots on leaves, and today i noticed that leaves are looking unhealthy, like discoloring.

I will upload some pictures soon, as im writing from Phone.

https://www.dropbox.com/s/rrvc11m6hpcrcmj/20140609_163904.jpg

https://www.dropbox.com/s/d4wwqetgzzvmw0q/20140612_112900.jpg

Looks fine to me?

Doest look fine to me. Look at those young leaves, discoloured arround and nicely green in the middle.

I think i will add calcium/mag nutes and will see how it will work out.

If your soil has been properly buffered with dolomite lime, you shouldnt need to adjust the PH of your water. You do need to adjust PH when you feed nutes. If you dont already have it, get some ph up ph down. As for testing the soil, go to Lowes and get a two prong soil PH meter. Most people here will tell you they are junk, but you need to know how to use it.
after using it a couple of times the soil will leave an invisible film on the prongs and it wont work corectly. to fix this dip it in a bottle of ph down or some lemon juice to clean the prongs then rinse with water and you are good to go.

I see nothing that would indicate a Ca or Mg deficiency in the pictures. The spots I see in one of the pictures looks like insect (probably spider mite) damage.

Dolomitic lime\garden lime neutralize acidity (raising pH); which isn't always what you want. In many areas, particularly in parts of western and sourthern United States, the tap water is hard, alkaline and actually already has Ca and Mg dissolved in it (as bicarbonates) due to deposits of limestone near the aquifers.

The river water may be a similar case; with minerals already dissolved in it. If this is the case applying lime isn't going to help (and there may not even be a problem). Even if applying nutrients, I doubt if you need to pH anything and if this is an in-ground grow that wouldn't help anyways. I grow in containers and don't pH anything ever, healthy soil pretty much keeps itself healthy.

Let me get this clear...

Your saying that I shouldn't even take measurements with ph meter and just add nutriets as allways?
Before an hour I watered my plant with river water which was 350ppm and added fertilizers which contained also Mg and for extra added N - Cal nutrients (both liquid) After adding a bit nutes, meter showed me 605ppm, is this ok?

Anyway, I will post some pictures tomorrow and show you how my babe is doing. Than I will see if nutrients were needed or not. I'm just afraid of overwatering now.

i agree, it looks like spider mites, i never ph water as the soil will buffer the water to the ph of the soil, though after a while the ph will change. treat for spider mites, and if problem persists add some epsom salts, 1 tea spoon disolved, then in your feed. and get some bio bizz bio grow organic fert, will give you everything you need, check the ph of your soil, the bag should say. and you might not want to use river water, at any time there can be contamination and ruin your crop.

Added Cal/Mag and everything looks fine now, now thinking about LST, do you think it's good time to LST?