Ok, I have some other questions to ask about my actual pH/TDS meter, but I'll take that back to the other pH thread later.

Results of my regular tap water are (drumroll please....)
pH 8.5
TDS 150ppm

That's pretty good, right? Would I be better off with the pH a bit lower? I tested some rainwater that I had collected, which was right around a pH of 5, so really basic. So, if I wanted to bring my pH down a bit, I could add some to tap.

Anyone know of a Paph specific pH list that shows the preferred pH of each species? I know Antec mentions a few but I haven't found another more comrehensive list in a short time of looking.

As previously mentioned, I have both forms of the MSU fertilzer on the way, so I'll be able to play around a little with this.

8.5 is pretty high, but 150 is not too bad. I would try a 3 to 1 mix of rain to tap and go up from there until you get the right ph. I would think around 6.5 to 7.5. The trick is to keep th ph stable, rain water does not have any buffers and the ph can fluctuate. The dissolved solids in tap water will provide stability.

I keep several 50 gallon drums full of water for the various fish I breed, some with with peat moss to lower the ph to 5 and below for a select few fish. Some with oak leaves to keep a ph around 6.0 for most of my fish and a RO/Tap mix of 3 to 1 for a neutral ph.

pH probes tend to have problems giving a true pH in rain and RO water because they depend on ion exchange across the glass membrane, and there are very few ions in pure water to drive the probe. So the rain water pH is probably closer to 7, which is neutral. Often you can change the pH of rain and RO water just by aerating it, and changing the gas balance away from CO2 to more O2 (pH will go up). It looks like there is a goodly amount of buffer in your tap water, and I agree with PB about diluting it down with rain or RO water.

Ok, I have some other questions to ask about my actual pH/TDS meter, but I'll take that back to the other pH thread later.

Results of my regular tap water are (drumroll please....)
pH 8.5
TDS 150ppm

That's pretty good, right? Would I be better off with the pH a bit lower? I tested some rainwater that I had collected, which was right around a pH of 5, so really basic. So, if I wanted to bring my pH down a bit, I could add some to tap.


pH 5 would be acidic, actually... Very pure water is very sensitive to dissolved gases which change the pH, there isn't anything in there to buffer the changes. It is the CO2 (which produces carbonic acid) that is lowering your pH. Like rick said...

But regardless, rather than trying to buffer your water by adding tap water, I would check the pH of whatever water you are going to be using (if you were adding tap to rainwater anyway, check whatever that mixture is), and adjust the pH. You can buy 'pH-UP' or 'pH-Down' at the local hydroponics store, although I would just use lemon juice or vinegar to lower the pH. It is hard to raise pH with things most people have in the house, I use KOH (potassium hydroxide) from the lab. That might be a good time to get some of that pH-UP stuff.

After you carefully adjust the pH to around 6 or 6.5 or so a few dozen times, you will get an idea of how much acid or base to add. Also remember that almost any fertilizer you buy will greatly lower the pH of the final solution. So you would need to add a different amount of base to bring that back into range.

As a practical matter, I stopped worrying too much about the water pH a while ago. It seemed that it didn't make much difference in my hands. I've always thought that the potting mix has far greater buffering capacity than anything we can add to the water. But others tell me I'm an idiot. That is ok... We are probably both right, the last few times I did check my water/fertilizer solution it was in a pretty good range already.

I wouldn't be too anxious to trust that TDS reading.

A TDS meter is just an electrical conductivity (EC) meter with a built-in conversion factor to ppm dissolved solids.

The problem lies in the fact that the specific ions in solution each have their very own charges and sizes (which affect mobility), hence contribution to conductivity, so that conversion factor is based upon a generic mix of ions, and may not have any resemblance to the reality of your situation.

I have two TDS meters, and using a standard conductivity solution and the data provided by the folks at GreenCare, I created calibration curves for each of them in their Orchid Special for Pure Water formula. At 125 ppm N, the theoretical TDS of the formula is about (if I remember correctly) 350 ppm. My two meters, by contrast, display 475 and 600 ppm in that solution! Some "standard" conversion factors, huh?

http://www.firstrays.com/Pictures/TDS_Calib.jpg

We also have to keep in mind that if we change the fertilizer, the calibration has to be redone.

Both Rob and Ray make very good points. I generally only check and adjust the pH of my fert. mix water to about 6.5 - 7.0. The pH of my makeup water is irrelevant since the mixture of all the goodies will impact the pH and conductivity in a unique way for your conditions. I actually prefer to use Protek to increase pH. Its just a fancy cleaned up potash solution. It's mostly potasium hydroxide, but it also has silicates in it, which can help build up cell walls for improved drought tolerance and disease resistance.

In my tox lab we use EPA moderately hard water. It has a pH of about 8.0, a conductivity of 325umhos/cm, and a TDS of 220ppm. For comparison 150ppm NaCl in RO water will have roughly a neutral pH (depending on how hard I breath on it), and a conductivity of about 300. In Los Angeles and Las Vegas, its not unusual to see over 400ppm TDS and conductivities of almost 2000umhos/cm, with pH still about 8.5.

So compared to an EPA benchmark your tap water has probably less dissolved solids than the average city water in the US, and is probably fine for your general watering needs. If its not inconveinient or expensive to thin it out with rain or RO I think that would be even better.

Thanks to all...I need to digest and parse this before I post a couple more questions. A little confused still.

Ray, I did find that info on your site this morning, and also your fertilizer calculator, which I am looking forward to using as soon as my fertilizer arrives!

Also, two easy questions:
1) do I really need this solution for the electrode? Didn't know that, sounds as if it may be important...

2) I totally don't understand the calibration aspect of this. I got the combo Hanna pH/EC/TDS 98130, if that helps. I don't understand WHY and WHAT I need to calibrate, nor do I understand what I should be calibrating it to! :?

Can you tell chemistry was not my best subject?

pH 5 would be acidic, actually...

Ok, I wasn't sure about this yesterday, so I looked it up, and it said 7 was neutral, less than 7 was basic, and more than 7 acidic, so is this wrong? Is it the opposite?

If the solution you refer to is a calibration solution you do need it. Especially for pH. The "brain" in the meter needs some kind of reference to compare unknown samples to, and it needs to have its "memory" refreshed at least once per day on the day's you use the meter.

As Ray was saying you may need to create your own standard for TDS due to the variability of ion composition in every water. Most store bought standards are either NaCl or KCl, and in the example I posted last, 2 samples with almost identical conductivities (i.e the MH lab water and NaCl std.) have TDS values that are considerable different. You could get the TDS value from your City water folks, who run TDS the real way (by evaporation and mass determination) and then dial your meter in with that value. Then as you add your fertilizer you'll see how it changes relative to your make up water.

No, for the electrode maintenance, it recommends a storage solution. Do I need this?
It also recommends a cleaning solution.

Then, indeed, you are right, there are all these calibration solutions! So, there are all these different choices and I have NO idea what to choose.

I had no idea I needed any of this! :shock:

EEK!

Paphgirl - below 7 is acidic and above 7 is basic

In general you want to calibrate an instrument in a range close to where you expect to measure your unknown solutions. With pH its best to do a 2 point calibration bracketing the values you expect to see in your unknowns.

Most people like to get there fert mix to a pH of about 6.5, so calibrate between 4 and 7. If you think your other measurments are going to be above 7 then calibrate between 7 and 10.

TDS/conductivity meters generally have just a single calibration pt. so just try to find a reference close to what you want to measure. As I mentioned yesturday you might want to use the tap water as a standard, and get the TDS numbers from the city.

I would expect the meter to have come in with directions on how to use it.

Thanks Rick, it did come with instructions, but very minimal ones on just HOW to set it but not what to base the setting on and I just had no clue so that was very helpful. I think I am beginning to understand better.

Heather do you have access to a decent gram scale?

You can make TDS standards pretty easy if you do, and many of the salts you could use for a custom mix are readily available.

NaCl (salt), MgSO4 (epsom salts), NaHCO3 (baking soda), CaSO4 (gypsum). I don't think you'd need to use lab grade materials to get "close enough" for what you want to do.

No, unfortunately, I don't. I have a good ounce scale, but nothing that small.

Update -
Okay, first, my meter does have a 2 pt. calibration, so I've just ordered the 4 and 7 calibration solutions. That said, obviously I haven't calibrated yet.

Today, I played w/ water, my sprayer is 2 gallon capacity, and 1 gal. distilled + 1 gal. regular poland springs bottled water, plus 125ppm/gal. of MSU fert. for pure water, and 1 per gal. of superthrive got me to pH of 6.5.

I also ordered some Pro-tekt to use instead (I hope) of the regular bottled water to boost the pH, and since I've had some issues w/ burning as of late, thought it would be a good choice.

So, we'll see how this goes for a while.
Thanks for all the help, everyone!!

Yippee!
Our local paper just published two pages on the town water report from 2004!
Now, I just have to decifer it! :D

Im my plants i had a problem cause the TDS was 120 PPM and PH 7.8 this water is from tap, this walter burn my roots , and breaking down !! So I change for rain walter and with TDS averege 15 PPM and PH 6.5 is so good , I have pictures this roots but I don´t know how do I put here !!