Clear Lake Jar Test


Abaena blue-green algae in the inaptly named Clear Lake

I have heard that there is only one place that is more difficult to produce drinking water in California than Clear Lake, and that is the Sacramento Delta. Those poor bastards.

Clear Lake has never been clear; a fact to which Livingston Stone, a fisheries biologist attested to in an 1873 report:

It is a singular fact, illustrating the inaptness with which names are often given to natural objects, that the water of Clear Lake is never clear. It is so cloudy, to use a mild word, that you cannot see three feet below the surface. The color of the water is a yellowish brown, varying indefinitely with the varying light. The water has an earthy taste, like swamp water, and is suggestive of moss and water plants. In fact, the bottom of the lake, except in deep places, is covered with a deep, dense moss, which sometimes rises to the surface, and often to such an extent in summer as to seriously obstruct the passage of boats through the water. – Livingston Stone, 1873

1. Blue green algae in water from shore of Clear Lake. Each jar has 1 liter of lake water.

It is a naturally eutrophic lake. As Lake County’s page on the lake notes, “Eutrophic lakes are nutrient rich and very productive, supporting the growth of algae and aquatic plants (macrophytes). Factors contributing to its eutrophication include a fairly large drainage basin to contribute mineral nutrients to the water, shallow and wind mixed water, and no summertime cold water layer to trap the nutrients.”

The algae in the southeast fork near the shore of the lake started look like pea soup this week. A biologist friend told me it is Anabaena, a blue-green algae. I’ll take his word for it.

I thought it would be fun to do a jar test on a sample taken along the shore line. Water treatment operators use jar tests figure out what dose of chemical will work best to flocculate (clump) suspended bits of microscopic stuff, which are easier to filter it out the water.

Each water system is different because water is different everywhere. Yes, H2O is H2O, but pure H2O is not drinking water. Drinking water has dissolved minerals and varies in pH (acidity/basic).


2. About ten seconds into the jar test, the jar on the far right (30ml polymer/1 L water) begins to flocculate and takes on a “blizzard” look.

I make no claims to being any kind of expert at jar testing. I will outline what I did. Your mileage will vary for your system.

  1. Scooped up a bucket of water from the lake and distributed one liter each to four clear jars.
  2. Mixed one millilitre of ProPak 9890 to one liter of filtered water.
  3. Placed the jars in the jar test machine and dropped the propellers in the water.
  4. Set the paddle speed for 100 rpm.
  5. Took 5ml, 10ml, 20 ml, and 30ml from the ProPak 1ml/1L solution. (The amount of solute to use is a “fielder’s choice.” It could have been 1, 5, 10, 15. The amount is a way to begin to bracket the right solution.)
  6. Dumped the 5, 10, 20, and 30 ml samples into the jars.
  7. Timed the event for 1 minute, spinning the mixers in each jar.
  8. Judged which (if any) of the jars developed a “flurry” or “blizzard” of flocculant. (See picture 2)
  9. Repeat as necessary to “dial in” the correct amount of millilitres of polymer to one liter of water. For example, I next might try 25 ml, 30 ml, 35 ml, and 45 ml to find out if the 30ml/L is the optimal coagulant mix.

Again, I am a novice and make no claims to being any kind of expert at jar testing. I just found very little on the web about how to do one, so I thought I would share my experience. If you noticed something I missed, or made a mistake on, or anything thing else that is as unclear as Clear Lake’s water, please leave a note in the comments or use the “Contact Page” to let me know how my jar testing could be improved.


3. Several minutes after the paddles have been turned off.

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