Hydoponics Water Quality and Water Treatment--A MUST READ!

You know where I tasted the best tap water? ARUBA! ...an island off the coast of Venezuela. Why? The island desalinated the sea water by distillation from the heat off their power plant. Smart, right?! The water came out of the tap distilled! I also bought some dank (...or not-so-dank) which included a sketchy exchange involving two dudes, one for money, the other for the bud.

When evaluating your grow, water quality is an important topic. Is it from a city water supply or well? How is your water treated? What's the TDS out of the tap? Is the water put through a water softener? Are you utilizing filtration systems? What kind of filtration?

In this article I talk about Total Dissolve solids, Reverse Osmosis Filtration, Well Water, Water Softeners, and Water Treatment. The last topic, water treatment, is a must read for everyone, even if you skim past the first topics.

Total Dissolved Solids (TDS)

What is Total Dissolved Solids (TDS)? It's the total substances (mineral or not) dissolved in your water. In gardening we use conductivity meters to approximate the TDS values of minerals in the solution. The meter contains two metal probes a current is sent across that a small computer calculates the conductivity or approximates the total dissolved solids (TDS) of your water. The meters usually include buttons or dials for calibration and sometimes allow you to change the reading between Total Dissolved Solids (TDS) or Electrical Conductivity value (EC).

The units of measurement depend on the meter and user's preference. TDS values are conventionally in "parts per million" (ppm), a value that is roughly equivalent to milligrams per liter (mg/L) of solution. Alternatively you can track the amount of minerals based on the conductivity in units of Siemens or, commonly, milliSiemens. If you want to dive into conductivity and how it works, check out Bluelab's article Conducitvity. Also check out Bluelab's FAQ's #5 "What PPM Scale Should I Use?"

I recommend cloning with water under 200 ppm on the 500 scale before nutrients are added. That is 0.4 millisiemens (mS) conductivity or 400 microsiemens (uS). Once you add nutrients to your water these values will increase depending on nutrient strength. Owning an EC or TDS meter allows you to track you water quality and nutrient levels. 

I personally log conductivity in microsiemens (uS) which is 1/1000 a millisiemen (mS). For customers I often will speak in terms of the more common hydroponic values milliSiemens (0.002 - 3.0 mS is usual) or ppm (1 - 1500, also a common range). I have operated grows with water supplies ranging from 60 ppm to 3000 ppm. The two higher values were 500 and 3000 ppm and were on rural wells tapping aquifers linked to limestone. These high TDS values out of the tap required filtration. 

When it comes to cloning, if your water is above 200 - 300 ppm I recommend Reverse Osmosis Filtration (discussed next). If your water is under 200 ppm, jump to Water Softeners and Water treatment. For cloning and hydroponics it is a must that everyone read about Water Treatment.

Reverse Osmosis Filtration (RO):

Reverse osmosis pushes your water through membranes with such small pores that ions can not easily pass through BUT most of the water can. There's a small amount of water that can't make it through referred to as 'brine' and contains the molecules and ions too big to make it through the RO membrane. Usually the brine tubing from your RO is black or some other color to indicate it is the unwanted water. I recommend using that brine to water your grass, top-off swamp coolers, or other application as apposed to dumping it down the drain. Installing an RO can seem daunting, but it's easy. If you're overwhelmed, work closely with the tech support of the manufacturer.

With RO filtration, if the source mineral content is high, your RO system (within a few uses) will only be able to reduce mineral content by 90%, leaving 10% residual. For example, if your water source is at 500 ppm, you may end up with 50 ppm residual mineral content. If a water softener is employed, that is about 50 ppm of sodium (Na+) ions. I discuss Water Softeners in the next section, along with an options to eliminate sodium in these systems. 

With your RO system, you can prevent this increase to 10% by changing your ion-exchange column (also referred to as a Mixed Bed Ion Exchange column). Simply change out the last column every time the TDS jumps back up to the 10% value mentioned above. Some mixed-bed ion exchange resins have a color indicator that changes colors when saturated. I don't believe the ion exchanger is necessary for water used in cloning unless your going through a Water Softener.

Water Softeners

Water softeners swap potentially “good” or unknown minerals for sodium ions. This is to protect your home appliances because sodium salts are very soluble and will not leave mineral deposit. While most mineral salts, such as calcium , will leave deposits and build up within appliances. Problem is sodium (Na) is not an essential mineral in plant nutrition or hydroponics. In high amounts sodium will antagonize or compete for uptake with certain nutrients, such as potassium (K). If you use a softener, take note of the TDS/EC of Sodium after the filter. If the 10% residual minerals is above 50 ppm, that is ~50 ppm sodium, you may consider regularly exchanging your Ion Exchange Column on you RO OR switch to potassium salts (KCl) in your water softener. Using potassium salts would make your RO flow-through potassium (K) instead of sodium (Na). Bags of Potassium softener salts are generally sold where sodium salts are available.

Water Treatment

By now you have water that is below 200 ppm minerals (or 0.4 mS TDS) AND the mineral content is plant safe (ie calcium or potassium). The next topic is water treatment. In cloning we prefer water treatment, while the results are different from city-to-city. For example, I found a suburb in Dallas, TX with ~4 ppm free chlorine on my test strips. This is 1 ppm higher than levels recommended for a swimming pools. Meanwhile in Austin the reading was undetectable. You can use chlorine test strips from a local pool supply to get to know your waters treatment level. I like the strip that tell you pH, alkalinity, total chlorine, and more...they're a great check-up for all your instruments, too. 

If you have tap water that's below 4 ppm Chlorine, or has undetectable free chlorine, I recommend your initial cloning water is boosted to 4 ppm chlorine. This is even more important if you're using well water. Here's the recipe: 

0.10 - 0.20 mL/gal of Bleach® (8.25% sodium hypochlorite) yields approximately 2 - 4 ppm of free chlorine and an ideal dose for UNROOTED cuttings.

1 mL = 20 drops; so 0.10 - 0.20 mL is 2 - 4 drops of 8.25% Sodium Hydrophlorite (Bleach®)

ALWAYS add oxidizing products BEFORE pH adjustment OR additives. “free chlorine” reacts with most hydroponic additives. Be sure to expose clean pH and TDS meters to this solution before additives to surface sterilize. Then, after all your cutting are in place, I recommend a second boost of chlorine but at 2 ppm (2 drops/gal OR 0.1 mL/gal) to surface sterilize your cuttings and sterilize any surfaces you contacted while filling the cloner. 

Hypochlorous Acid products like Watermax™, UC Roots™, and Clear Rez™ are effective at 10x – 100x lower chlorine concentrations than hypochlorite salts such as Pool Shock (calcium Hypochlorite) or Bleach (Sodium Hypochlorite). Hypochlorite products are NOT the same as Hypochlorous acid products. Hypochlorite product (such as pool shock or bleach) require .5 – 5 ppm free chlorine to effectively sterilize plant roots systems or cuttings while Hypochloruos acid is effective at 0.05 – 0.5 ppm. These product are also most effective before additive and using the same pre- and post-boost dosages. Good news is you're running much lower chlorine levels. 

What I like about working with hypochlorite salts (Pool Shock & Bleach) is I can use cheap pool test strips to help verify I am in the 2 - 4 ppm free chlorine range. AND REMEMBER, all low-dose oxidizers (including hydrogen peroxide) should be added before and AFTER ALL cuttings are in place BUT and ALWAYS prior to additives OR pH adjustment. This ensures their oxidation potential is properly focused on your system and cuttings.

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