DI water, pH, TDS, fertilizer, KOH, ProTekt, TRIS?

[tropterrarium]

Just measured the pH from my DI water and it is <4, a tad acidic. There are several options of adjusting it:
- add tap water, about 25% of DI volume, gives pH of ~6 (I use a simple drip/color match test) and TDS of 50 ppm.
- I could add KOH, work in a lab, so easy to get some. Given that DI water has very low buffering capacity, I wonder whether it will go from 6 to 10 with a single drop of 1N KOH. Haven't tried that yet. Any experiences? Will skew the npK ratio a bit, but don't think that matters.
- There is also the infamous TRIS buffer. Have not seen anything about it re plant water, so wonder whether anybody has tried that.
- Dynagrow has a pH-up adjuster (Protect), most likely a buffer like TRIS, just at a higher price. So, worth it? I use Dynagrow liquid fertilizer, so that should be compatible.

What do you do? Any experience, good bad ugly?

[zxyqu]

Well, what is the pH when you add the appropriate amount of fertilzer? Often, this will push it a little in one direction or another. Also, Ray sells a general hydroponic pH up/down (2 products, likely similar to Dynagrow's). In your case the pH up should push the pH into a more acceptable 6 ish range. This would probably be my first choice one you figure what it will be with the added fertilizer.
I work in a lab as well, so in light of your idea for potassium hydroxide is well place, but I wouldn't put anything from my lab in with my orchids. But, it could actually work. I'd make a more dilute, .1 or .01N solution, and that should get around the pH jump. Also, adding it once the fertilizer is in will help with the buffering.
Adding tap seems to take away the whole idea of DI water, but make sure you add a DI based fertilizer that accounts for less salts in the DI water.
I have no idea of adding TRIS, seems pricey given your access to KOH if you really wanted to go the lab route.
Hope that helps some, but sounds like you have some options that should work fairly well. Good luck, and let us know what you decide.

[tropterrarium]

there are two slightly separate issues:
- watering water (no fertilizer added).
- water with fertilizer.
Generally, fertilizers are on the acidic side, so will push certainly down from 6-ish. here https://www.msu.edu/user/harveyb/Fertilizers.htm is a nice summary. We have ACS reagent quality, or DNA grade chemicals in the lab, so I have not the slightest issues with using those. Re TRIS, free off the shelf is still way cheaper than anything I buy ;-).
Going lower N with KOH is possibly wise. If I can get away with a few drops per gallon, that would be the ideal concentration for the stock solution. Not that hard to make three stock solutions.

[zxyqu]

Very true. If you trust your lab, go for it. I'd imagine the buffering capacity of your non-fert water will require less KOH. I'm intrigued at how well this will work. One of those "duh, good idea" moments that I've disregarded. I think the fert-water will still raise the pH from your current 4 ish into the 5ish range (depending on your fert), but still may require some pH/KOH to bring it into the 6ish range. This is gonna be a fun experiment. You should also break out the pH strips from the lab... ha

[tropterrarium]

pH strips are *vintage*, so rather go to Sotheby's. I got a drop solution - color kit a the local hydroponics shop. Not sure I want to spring for a pH meter, may be too much trouble (calibrating solution, taking care of probe, ...) than worth it. Within 0.5 pH units should be fine. I grow a variety of species, so not that critical to adjust to the last decimal.

[Ray]

Pro-tekt is a potassium silicate solution intended to "beef up" plants for insect protection (I doubt) and warmth tolerance (anecdotal evidence that it works), that just happens to raise pH. It would be a good choice for the plain DI water.

If you use an typical "off the shelf" fertilizer that is intended for use with mineral-bearing water in your DI, the pH will plummet even more. If you use one formulated for pure water, you may not have to adjust the pH at all.

[tropterrarium]

Hi Ray,

thanks for the info. I will gladly take the side effect of protect. Re pure water formulated fertilizers, do you have any recommendations?

[zxyqu]

Ray sells a MSU fertilizer for DI/RO water on his website. I actually dont know of any others, but I haven't been in DI/RO water for long.

FirstRays.com

[King_of_orchid_growing:)]

How about baking soda?

[keithrs]

I personally think adding de-chlorinated tap water will be the best way to adjust your PH..... You will be adding a small amount of cal and mag back into the water too.

Not sure if your going to store your water but PH buffers will lose there effective-ness over time and you'll get PH drift which is bad if you per-mix or store your fertilizer as a "ready to use" solution. Every time you get PH drift you'll get elements that fall back into salts which then become useless to the plant.

Also, correct your PH of your water before adding fertilizers. PH up or down can be used to correct your fertilizer right before use. If you see a cloud when you add base or acid.... thats elements falling out, back into salts.

I'm experimenting with Technaflora BC grow fertilizer with a calmag supplement. So far its works great for growing but have not used it long enough to see how it flowers..... It is a very PH stable fertilizer and the amount I use I have not had to adjust my PH.