Water Chemistry Made Simpler by Bob Lusk

Okay, you’ve perused the pages of Pond Boss for years and have a good understanding of pH. You get that a pH of 7 is actually zero and that for every point you go down, the acidity of the water drops tenfold. That means a pH of 6 is ten times as acid as a pH of 7. It also means a pH of 5 is 100 times more acid than pH of 7. Going the other way, it simply means stuff dissolved in water is influenced by a base, maybe calcium carbonate…lime. Same concept, though, regarding the ten times thingy.

And, you understand the value of alkalinity. Alkalinity is simply considered the amount of limestone, calcium carbonate, dissolved in your water. But, Total Alkalinity is a measurement of the quantity of all bases in your water. That could be bicarbonates, sulfates, carbonates, phosphates, and hydroxides.  All of these are natural in your water, coming from sources dissolved via minerals in the soils or from byproducts of biological processes from decomposing of organic matter. To keep it from becoming too complicated to understand in case you aren’t a chemist, the value of alkalinity simply measures the pond’s ability to be productive, to grow plankton, and give animals the goodies they need to form bones, shells, and scales.

Hardness is basically a measurement of the overall concentration of salts, or those positively charged ions in your water. Those are normally iron, calcium, magnesium, sodium, and a handful of others. While hardness is a collective measurement of these salts, it doesn’t really tell you where they come from. For example, in our ponds here at LL, 2, the iron measures a little bit high. That’s due to two things. We are surrounded by iron ore rock in the soils, and our well has high amounts of that orange stuff. 



Here’s where the proverbial curve ball comes in. When a pond has all this stuff dissolved in it, we can certainly measure it, but what does it really mean when we boil it down to your management strategy?

Well, water chemistry directly influences what happens in your pond. If alkalinity is low, say lower than 20 parts per million (ppm), then your pond’s ability to grow fish is limited. They don’t have all the minerals they need to properly develop. Taking it a step further down the food chain, plankton doesn’t have the ingredients they need to thrive. You can fertilize that pond until the cows come home, but if the alkalinity is too low, don’t expect plankton to grow. Marginally low alkalinity and low hardness might stimulate that plankton bloom, but the pH can swing from 7-10 through the course of a warm day. That’s a one thousand fold change—stressful to creatures in the water.

With alkalinity from 50-150 ppm, the water is buffered. That term simply means the water has plenty of Rolaids in it to keep any acids from pushing the pH downward into that acidity side.

What’s dissolved in your water has an impact on its ability to grow different plants and support different invertebrates and fish.

So, when a biologist or your lake management consultant suggests you have your water chemistry checked, they want to look at the fundamentals, first. pH, alkalinity, and hardness work together to afford your water its ability to produce life. Secondary to those elements, we want to look at the nutrient load. That’s a measurement of how much nitrogen, phosphorus, and potassium is dissolved in the water. That’s a totally different set of parameters.

Combined, all this stuff allows you, and your pond expert, the chance to see what influences the biology of your pond. Different combinations of these various salts, metals, and minerals work to create the basic environment in your pond and can be the cause of the effects you see manifested.

Okay Lusk, what did you just say?

Here’s the drilled-down version.



The green color of your pond is influenced by minerals and metals dissolved in your water. Those same minerals directly influence whether your pond is muddy or clear. The species of plants you have are tolerant of what’s dissolved in your water column. Combining with those minerals and metals are the different nutrients. If you don’t have the minerals, metals, and nutrients, cattails won’t grow. Neither will your fish.

Water chemistry is important and just as complicated as you wish it to be. Have your water tested periodically. Most every land grant university in the nation has a water analysis lab—usually the same one where we send soils to be tested. Check with your county agent or dig around online and find the best lab.

When you get your results, look them over. Start with pH and then alkalinity. If your pH is between 6-8, it’s well within the bounds of what you want. You can still be successful outside that range, but you might need to amend your water a little bit. If your alkalinity is more than 20 ppm, you’re good to go. Beyond that, ask for an explanation to see how the different values impact your ecosystem.

Just because this stuff seems pretty complicated doesn’t mean it won’t have value for you. When you do have a problem, the first thing you’ll want clarity on is your water. 

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This article was extracted from the Nov/Dec 2013 issue.

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