OrchidSafari
Water Quality
Questions and Answers
By John G. Talpa

Q) Will water that is too basic (7.8 - 8.0) make nitrogen, calcium, mg, etc *unavailable* to plants/orchids? Our municipal water supply typically runs in the high 7's to low 8's. I've been trying to bring the pH down between 6 - 6.5 but it's not practical to do for daily watering of bareroot vandaceous, etc. I use rainwater for fertilizing in warm weather but no way to heat it in winter. I am seeing some chlorosis & wonder if it's the high pH.
Sandy Hardy
Savannah, GA

A) I doubt that the problem is with the pH. In my area, the well water runs between 7.4 and 7.8 and the plants grown on raw water are doing quite well. With all of the different fertilizers available, there is no way of knowing if a particular formulation would not perform well with a pH of 7.8-8.0. I would expect a fertilizer manufacturer to state that the product should be used within a specific pH range if that was critical. Now, the plants might not appreciate the higher pH, but the fertilizer should be okay. It would be best to check with the fertilizer manufacturer.

Q) My question for John is about RO. Do you need to add anything back to it and what? I'm concerned with minerals such as calcium, etc. Would a hydroponic fertilizer add what is taken out?
Karen

A) Overall, this would be plant specific. For example, some Paphs like higher amounts of calcium so many growers add lime, oyster shell, etc. to their mix to keep higher amounts available for those plants. Some growers use a small amount of fertilizer in their water at all times. Most hydroponic fertilizers have very low concentrations and should be fine for most plants on a continuous basis. If you are in a hard water area, you can even add back some raw water to buffer the water, raise the pH a little, and add some of the minerals you remove with reverse osmosis.

Q) I have had my water tested twice, by a local laboratory. It tests about 455 PPM. Half or about 250 PPM is NaCl. There is plenty of calcium and a touch of iron. I do not have a water softener, it's how it comes out of my well. I always have problems raising any thin leafed orchids. Catts and phals tolerate it pretty well. I use an excellent grade of aliflor from Germany, so I water every other day. I use between 40 and 50 gallons of water per watering. I may build another greenhouse, but that's about a year away.

While my plants grow extremely well, I know RO water would take me to the next level. I plan on buying a 225-gallon poly tank for storage.

My needs are....... How large a unit do I need, and what brand do you recommend? I plan on running the water through a Dosatron...again what do you recommend? Last but not least, I will need a pump to push the water through all the above and out the garden wand...any suggestions on type and capacity. We have Grainger's locally, but can go elsewhere if need be. At present I use a 30-gallon trashcan and a 1/2 HP sump pump.

At present I have a 14X37 foot greenhouse that's about to bust with plants. I may build another in the future. I'm looking at 20X60 next time!

Thanks,
Dan

A) Kathy, I had answered Dan's questions in private emails prior to his posting on your forum. Here are some of the highlights:

I recommend a reverse osmosis system that uses at least a 100 gpd membrane. Most manufacturers use water that is 77F at about 60 psi to test their membranes. Since the temperature on site is about 55F and pressure is less than what the membrane is tested at, I would estimate actual production at 50 gpd.

If Dan would expand his greenhouse, he would need about 2.5 times what he is using now. If the new greenhouse is in addition to the existing unit, he would need 3.5 times the current amount. Raising the temperature to around 80F and adding a properly sized pump will produce 100 gpd. This will handle his requirements if he uses water at the same rate.

On the other hand, if Dan decides to use RO water for misting, he will have to opt for a high pressure, higher output, commercial unit. I think that in general, we tend to underestimate the amount of water we use.

The least expensive way to store the water is in an atmospheric tank. The bladder tanks are costly when you consider how much water is used at one time. Also, when you look at a 25 gallon bladder tank, it seems quite large. But, the actual amount of water storage is less than 10 gallons. So, you would need larger tanks and multiples of them. The costs add up quite quickly. A large atmospheric tank is relatively inexpensive and a sump pump can be used to dispense the water. The pressure should be sufficient to run the dosatron. Another way is to use the atmospheric tank connected to a repressurization pump and a single bladder tank. This would maintain a more consistent pressure and water flow for watering. Also, the tanks should be kept in the greenhouse if possible so that the temperature of the water is the same as the plants. The negative is that the water temperature could be too high during a long hot spell in the summer.

It is always difficult to balance the ideal system with the money we are willing to spend. With RO systems, I always recommend a larger unit than what seems adequate at the time. When smaller units are decided upon by the consumer, I often have to go back to add a second or third tank and/or a larger membrane because more water is consumed. We will find more and more ways to use the water. With orchid growers, this is especially true!

Q) Is there a working standard for greenhouse water quality - preferably showing upper and lower limits for major elements? We've had an unrealistic standard from Ohio State for many years but it has no relationship to what one might reasonable expect.
Thanks - Ed Wright

A) I have not seen a standard in use. I have several greenhouse customers and they seem to work with their County Extension Agent and the fertilizer manufacturers to determine what they need to do for specific problems, but I know of no one that really works from a standard.

Q) OK, I've got some questions on water chemistry.
People will often say: pure water isn't a good 'buffer'. Or: pure water is very acidic - or maybe they mean corrosive. (These comments usually occur in conversations about r/o water.) Boy, when I was in college we were taught that water was pH neutral (7) and that it was an excellent buffer, as it could donate either a OH- or an H+ (or proton donor, electron donor, which ever way you want to think of it.) Indeed it was a complex molecule with unique properties. (max density at 4C, its polarity, etc) What am I missing? Can you talk a bit about the chemistry & dissociation of water?

Also, knowing pH is important for some orchids. Can you talk a bit about cheap, ubiquitous pH test strips? Like, are the ones for pool testing adequate or is the accuracy range laughable for purposes of growing orchids? What would you use to check pH of your water or fertilizer solutions?

And: Many people use TDS meters to check their water purity. However some go a further step and test its conductivity, in either microohms or microsiemens. My water department will include conductivity in its annual water quality report. What is the difference between TDS and conductivity? Why would 'conductivity' be a more important item to know about one's water? Is there a conversion (or equation for conversion) from TDS to conductivity? (Or indeed any relationship at all?) Perhaps you should just talk a bit about conductivity, what it is, how to measure it, why its important - if at all - in your opinion.

Thanks,
Kathy Barrett

A) Most of the RO water that I have tested ends up being in the pH 5.8-6.4 range. So, it is acidic. However, it is normally aggressive (corrosive) because of dissolved oxygen and carbon dioxide content. The CO2 is what will also cause the water to become more acidic. For this reason, once the RO water is produced we normally keep it in plastic lines. Some places use stainless steel lines, but most of us cannot afford that.

In most homes, the water lines are made of copper. RO will take copper off of the pipes and cause pinhole leaks. I've heard of that happening in as little as a few months. Also, many older homes have copper lines that were soldered together with leaded solder. RO can pull lead out of the solder.

2) Buffering is the ability of the water to maintain its pH. Water with low total dissolved solids has almost nothing in it to maintain the pH so it is unbuffered. Adding an acidic fertilizer to RO water will cause the pH to drop further than in a buffered water with the same pH as the RO water.

This leads into your question about test strips. When I am testing an unbuffered solution, I have to use a special test strip. A standard test strip and the normal liquid drop type solutions will change the pH towards the indicator's pH.

3) Normal pH test strips will work fine for testing the water after fertilizer is added. In my observations, the average person will not take proper care nor do the calibration necessary to maintain accuracy with a pH meter. The most imporant thing with pH test paper is to keep it away from moisture, acids, strong bases, chlorine, etc. So, just keep it in a sealed plastic bag. A pH paper with a range of 4.5 to 7.5 is available. The main drawback of test strips is that the pH is in 0.5 increments. If you are satisfied with the pH being between 6.0 and 6.5 rather than 6.0-6.2, they are fine.

A color comparator with liquid indicator will have increments of 0.2 except for wide range comparators which are 0.5. So, if you wanted a pH of around 6.2, you would use an indicator like Chlorophenol Red which has a range of pH 5.4 to 6.8. The only problem I can see here is if the fertilizer has a enough dye in it to distort the color. The big thing with liquid indicators is to buy fresh indicator and keep it cool. The reagents I sell come directly from the manufacturer so that they are fresh. I've often seen test kits that are two, three or more years old being sold. In most cases, your guess at the pH of the water/fertilizer solution will be more accurate than a test kit with out-dated reagent. If you keep the indicator reagent in a hot greenhouse in summer, it could deteriorate in a few weeks.

Also, you have to use a clean stopper to agitate a sample using liquid indicators. Most people tend to use their finger and the skin oils and other contaminants on the skin will often change the pH enough that it won't be accurate.

Since I use this type of equipment in my work, I would use a meter. But, I am comfortable using a quality liquid indicator color comparator. For generalized use, the strips are great.

4) TDS is total dissolved solids. The way to check the actual TDS, is to weigh out a given amount of water in a tray, put it into an oven, evaporate the water, then weigh what's left. Conductivity is used because when a solid dissolves in the water, it increases the ability of the water to conduct electricity. So, increased conductivity of the water indicates that more is dissolved in that water. When you are using a meter, you are checking conductivity no matter what the units are on that meter. The meters are just calibrated differently for different units. As you can see, the meter is a much quicker way of determining TDS.

Micromhos (mmhos) and microsiemens are the same units. There are different standards for converting conductivity to ppm. The 442 Standard results in the following (this information came from Myron L):

a) 300 ppm = 447 mmhos
b) 500 ppm = 733 mmhos
c) 1000 ppm = 1414 mmhos
d) 1500 ppm = 2070 mmhos
e) 3000 ppm = 3920 mmhos

Let me know if I need to clarify any points.

Q) John, We have very good water (32 ppm. TDS, 8 ppm Mg, 9 ppm Ca) which has essentially no buffering capacity. What would you recommend using to adjust the pH up when using fertilizer such as Cal-Mag?
Janette G Harris

A) Janette, There are products at hydroponics stores, aquarium shops, and some garden shops called "pH Up", etc. They are normally solutions using sodium hydroxide, potassium hydroxide, potassium carbonate, etc. It would be better to stay away from the sodium compounds because of the potential damage to the root system.

A commercial product is the safest way to do this. If you obtained concentrated forms of the hydroxides, you would have to be EXTREMELY carefulin their use. They are highly reactive and can cause serious damage to your body that does not heal very quickly.

I've found that Dyna-Gro's ProTekt raises the pH. Starting with RO water that was pH 6.1, I added 1/4 tsp of ProTekt and the pH went up to 7.8. Then I added 1/4 tsp of Dyna-Gro 10-5-5 and the pH leveled out at 6.6.

Q) I'd like to ask a few questions if they have not already been asked.

1. Considering the wide range of prices for conductivity meters, what does the average hobbyist really need in a conductivity meter? e.g., What range should the meter be able to measure?; What degree of accuracy is needed?; Which styles are more durable? etc.

2. Regarding rainwater, how do you know if there are contaminants from the roof and/or smog that would harm the plants? Or is this not a problem?

3. Are there any orchids that should not be treated with epsom salts?

4. For measuring pH what are the pros and cons of dye indicators vs meters?

5. What are the pros and cons of tds meters vs conductivity meters? Especially, does one type of meter tend to be more accurate than the other?

6. Is there a source where one can compare brands/models of tds and conductivity meters? If not, what criteria should I use to objectively compare between different brands/models?

Thanks,
Charlotte

A) Part 1 - A good, accurate, reliable TDS meter starts at $150. There are many companies that now have the 'pen' type TDS meters under $20. They are accurate enough for what most growers need. I've seen them last from less than a year out to several years. A lot has to do with how they are treated and maintained. As I stated in a previous reply, they are all conductivity meters no matter what the units are on the meter.

Part 2 - A safe assumption is that there are things on the roof that are not good for the plants. Most of the people that I know that use rain water, let the first water from the roof go to drain or out into the yard. Then they move the downspout to fill their tanks. This will flush off the bulk of the impurities that could cause problems.

Part 3 - I don't know of any plants that cannot be treated with epsom salts. However, this question should be answered by a more experienced grower. All the recommendations for the use of epsom salts that I have seen have said that they should be used sparingly. Some have even said only once or twice per year

Part 4 - Answered in a previous reply.

Part 5 - All TDS meters are conductivity meters.

Part 6 - I don't know of a site comparing conductivity meters. Most meters within a given price range will be comparable. More costly meters usually have greater accuracy and longevity. You would compare the range, margin of error, warranty and cost.

Q) Well not directly a water question. More a water collection problem. I lack the word for the pipe like thing that collects water from roof. Mine are made of tin, which I know isn't good for orchids, but are their other materials to be avoided, also when it comes to the roof material it self?

How about water storage? How long can water be stored and what is the best way and is it necessary to use ultra violet light...

Maybe also a bit about R/O water and it's lack of buffering capability. What is it that is removed that now is lacking? Would a mixture with ordinary water help?

Just the few questions on my mind.

I am looking forward to seeing all the questions and answers on this most interesting subject.

Kind regards
Karen Frederiksen

A) Part 1 - There are many types of materials used in roofing around the world. I do not know what is in all of them. As I stated in a previous reply, the best way to use water from a roof is to allow the first water to drain away. This will flush off most of the impurities. Then fill the tank(s).

Part 2 - Water storage can be a problem. It would depend on the type(s) of biological organisms in the water. Off hand, I don't know of anyone that is treating their rainwater. Using the proper amount of chlorine or bromine, ultraviolet light chambers, or ozone would definitely help keep the biological growth in control. If I decide to use rainwater in the future, I will do that. Of course, I tend to be more cautious.

Part 3 - Buffering was covered in a previous reply, but, basically, RO removes almost all impurities from the water, so there is nothing in it to maintain a given pH. Mixing raw water into the RO usually will buffer the solution. But, it would also depend on the quality of the raw water.

Q) Please explain reverse osmosis. I understand osmosis: the movement of a solvent across a membrane [that holds back the big molecules] from a solution of greater to a solution of lesser concentration. Is reverse osmosis a double filtration system?
Thanks,
Sara Stephens

A) With reverse osmosis, you are applying pressure to the solution with the greater concentration. This allows the water to go through the membrane while the concentrate remains on the pressurized side of the membrane which then goes to waste. The pressure provides the force for the movement of the water across the membrane.

--The end