Acceptable ppm

Slippertalk Orchid Forum

Help Support Slippertalk Orchid Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Well-Known Member
May 27, 2007
Reaction score
I just bought a TDS (total dissolved solids) meter and took a reading of my well water. The reading was 204 ppm. Is that an acceptable amount of dissolved solids before fertilizer or should I invest in a filter or something to take more of the solids out?

Actually that's really good in my opinion. 204 from well water? Well water tends to be high, high er than city water but you number is really good.

Take a reading after you add the fertilizer though. You should stay below 500 ppm with the fertilizer. If the reading is higher than that, then you may need toadd less fertilizer or change brands/formulas.

Now let's go nuts... what is your pH level?

But seriously, your well water would make me happy as a clam.

Good luck,
Christian, central NJ
TDS meters are simply cheap electrical conductivity (EC) meters with a built-in conversion factor. The true conversion factor depends on the ions dissolved, so the conversion factor should change with each chemical composition tested. I recommend against relying on the number as "gospel", unless it's been calibrated, but it's still usable:

Many orchid growers use a measurement of "X teaspoons per gallon". Generally, powdered fertilizers are in the neighborhood of 1.5g/teaspoon, which means an actual contribution of about 400 ppm TDS per teaspoon used. Yeah, chemically-bound water in the hydrates used in the fertilizer formulation will reduce that a bit, but it seems like a thumbnail guide in that range is OK.

Let's say you're using the GreenCare MSU formula for well water and want 125 ppm nitrogen. That would require about 1/2 teaspoon per gallon, so you should see about 200 ppm added to your baseline, water-only number.
It's probably fine for most orchids, especially if most of the TDS is from calcium/magnesium salts. If all the TDS is from sodium bicarbonate then that's not good.

Can you get a pH and hardness value on that water too?

There might be some picky phags and pleurothalids, but most paphs would not object.

Latest posts