tap water profile

Hi all. Long time onlooker, first time commenter(I hope I'm in the right place, if not please let me know)
I've had an issue with my last two grows that I presume to be a deficiency, both times manifesting itself about 3 weeks into flowering. I know this may be unorthodox, but I'm not going to describe the problem or post pictures. I don't want to invite further uncertainty by receiving a bunch of varying, conflicting answers. I just want some help interpreting my tap water profile so I can compensate and adjust accordingly.
First, the relevant info:
-Soil grow, 5 gal. pots( Fox Farms OF, dolomite lime, perlite)
-Humboldt natural grow(3-1-3) and bloom(0-10-0), Liquid Karma, CalMag(haven't settled on a nutrient line, using what I had available)
-Ph everything to 6.5
-Atmospheric conditions are on point
-No pests
Though I've use RO water in the past, I've recently moved, and for logistical and ethical reasons I would prefer to use tap water. I have well water and I know it is soft, so I assume I should treat it more like RO than typical tap water. I'm just not sure which minerals specifically should be compensated or what is lacking in the nutes I'm providing.
So here goes: PH-4.9, TDS-73, EC-.12, Sodium-16ppm, Potassium-<1ppm, calcium-8ppm, magnesium-2ppm, total hardness-28, nitrate-<1ppm, sulfate-2ppm, chloride-28ppm, carbonate-<1ppm, bicarbonate- 3ppm, fluoride-<0.01ppm, total iron-.02ppm, total alkalinity- 3.
Can some experienced growers with comprehensive understandings of water profiles please help me out? Does anything stand out in this profile? Any instant red flags? Does this water, in conjunction with the nutes I'm providing, suggest a need to supplement any particular nutes/minerals? Please, no irrelevant guessing, rumor citing, or wild speculation. I don't want to waste anyone's time, I'm looking for some specific answers from a specific group of people. Some clear, thoughtful, expert answers would be much appreciated. Thank you very much.

All you need to look at is Ca and Mg...and those are low enough so you can treat it as RO. Supplement Ca and Mg with Calmag to around 200ppm. Add nutes and ph. Simple as that.
JD

Thanks for reply, JohnDee. I'm already doing that to no avail. Nothing else stands out to you?

Larsen,

I'm wondering what's causing that low ph of 4.7. And what are you using to raise it?

Na is always a problem and can displace K causing K deficiency. Is that what you're seeing?

Are you doing anything to the water once it leaves the well? Water softener?

You may just have to bite the bullet and buy an RO filter to clean out everything and start from scratch like many growers do...
JD

John,
Not sure why my water has such a low ph. I think it is a common ph for the ground water in my area...I blame glaciation. I'm not treating the water with a softener but I think you might be on to something: I use Earth Juice Natural PH Up, and often require lots of it to get to 6.5. This may in fact be displacing K with too much Na and causing a deficiency. As I stated in my original post, I didn't want to describe deficiency, but I was leaning towards a K deficiency. This might also explain why I didn't have this problem in the summer: ground water in my area is harder and ph is higher in warmer months, so I required less ph UP. After adding my nutes I'm usually in the mid to upper 5's for ph. Maybe I'll forgo the UP and add incorporate a bloom fert with potassium and see what happens. Thank you so much! I never would have considered the adverse effects of ph up.

Larsen,
I hope that helps you resolve your problem. I do hydro and one thing you get to know is water. I believe many "PH UP" products contain potassium hydroxide...so you'll get a little K boost along with raising the ph.
JD

Larsen said:

Hi all.... I don't want to invite further uncertainty by receiving a bunch of varying, conflicting answers. ... Thank you very much.

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Does anyone think 16 ppm of sodium in my tap water could be problematic?

L,
That's what I was referring to in my post above where I stated the Na can displace K. It does seem to be more then you'd like...but sorry, I don't have any actual figures or references to back that up.
JD

John,
I later realized that was what you were referring to but it raised a whole new question for me about ph up and potassium bicarbonate. Now I'm back where I started and would love some input on acceptable sodium levels. Thanks for replying.

L,
Potassium bicarbonate doesn't have any sodium in it. The bicarb component is HCO[SUB]3[/SUB][SUP]&#8722;[/SUP] but if you add a sodium anion to it...then you get sodium birbonare (baking sode).

To put it simply...
Potassion bicarbonate...GOOD
Sodium bicarbonate.....BAD

Far as if 16ppm of Na is too much...well I still don't know but will let you know if I find out...
Cheers,
JD

Thanks for your help, John. I'll keep you posted on my progress.