Water Quality, Part 2
What's in Your Water?
By Bob Lusk
Water is a fascinating substance.
Scientists call water the "universal solvent". Anything that can dissolve into water, will. The science behind this amazing fact centers on the bond between the two hydrogen ions and the single oxygen molecule. I promise, no chemistry lecture today. Just good, old fashioned common sense. There's some electricity going on, here, in this magical substance, H20. The hydrogen's have positive charges and the oxygen is negatively charged. The two act like magnets, holding on. But, when contacted with other compounds, such as lime...calcium carbonate...those gentle electrical charges act to dissociate that mineral and dissolve it, since the calcium has a positive charge and the carbonate is negative...and water has similar gentle, attractive charges.
Pure water has nothing dissolved in it.
Here's an interesting fact. Pure water doesn't conduct electricity. It's actually an insulator. Here's another interesting fact. We never come across pure water. It goes back to that "universal solvent" thing. Inevitably, something dissolves into water. Much of that dissolved stuff does conduct electricity. That's why we don't drop the hair dryer into the bath tub. It's what's dissolved in water that conducts electricity.
For our ponds, we pay attention to some of what's dissolved in the water. Water is the vehicle...what's dissolved into it is transported and utilized in the biology of the pond. One of the fascinating facts about this concept is that our water is constantly changing. It's changing what's dissolved in it, changing the biology and chemistry, which then acts to influence the rest of the biology...our fish and plants.
Here's what I mean.
As pondmeisters, we are taught to pay attention to pH, temperature and oxygen. Temperature influences water density. Density influences water's ability to hold oxygen and keep other compounds in suspension or dissolved. For example, I'll always remember a pond that got muddy each spring, stayed muddy all summer, then cleared late each fall and stayed clear all winter. I thought maybe that happened because that pond had a bunch of catfish in it or something. Nope, that wasn't it at all. In fact, there were no catfish anywhere near that pond. It was a reaction between the water and tiny particles of clay. The density of the water impacted its ability to keep the clay in suspension. Density changed with temperature.
As good pond managers, we are also compelled to learn about alkalinity, hardness, minerals and metals.
Think about it...we've seen and heard of all kinds of weird stuff dissolving into water. Lime is most common, but how many times have you seen well water spew orange stuff onto the ground? Iron. What about that faint rotten-egg smell sometimes associated with water? Sulfur.
For pond purposes, we need to know about alkalinity. Basically, alkalinity is a measurement of a pond's ability to buffer. Alkalinity works like Rolaids. Its nature's antacid. But wait, there's more. Alkalinity is important because of its biological effects, too. Certain important types of plankton need alkalinity in order to grow. When we consider fertilizing a pond, we want alkalinity to be at least 17, preferably 20 parts per million or more, or the pond won't accept a plankton bloom.
Typically, alkalinity is measured in the form of carbonates, bicarbonates and sometimes hydroxides. Most of the time, our ponds are influenced by carbonates, in the form of lime. That's why biologists recommend liming ponds with low alkalinity and low pH.
What's important to you is this...you need some alkalinity.
What about hardness? You've heard all your life about hard water. What's hard about water? Hardness is a measurement of minerals or metals dissolved into water, typically calcium and magnesium. Those are the two most common, normal positively charged minerals that make up hardness. See the relationship with alkalinity? Lime is calcium carbonate. Carbonate adds to the alkalinity, calcium increases the hardness.
We never come across pure water.
Moderately hard water in your pond is good. Fish like it. So does some species of plants.
What about metals in water? Most metals we find in water come from groundwater, via a well. Iron is the most common. But, there are some salts which yield metals, as well. Sodium chloride, table salt, is a common ingredient in freshwater ponds. The sodium is actually a metal.
Don't worry about having different elements of minerals and metals dissolved into water. Most of them are naturally occurring substances that blend to help the plants and animals in your pond.
Here's your word of caution today. Almost every single problem which manifests itself as a natural fish kill starts off as a problem with the water. Too much of this, or too little of that or too rapid a change with something in water is what often becomes an issue that leads to an abrupt change in your pond, which results in a fish kill.
Ask most biologists what caused your fish kill and you'll usually receive the following statement... "Oxygen depletion". While that's probably true, the problem wasn't simply that your pond had a shortage of oxygen. There's a reason for that shortage that can be tracked back to some consequence of a change in the quality or chemistry of the water.
Let's bring this discussion full circle. Your pond pH is perfect...near 7.0. Alkalinity is 55 ppm, well within the bounds of excellent quality. Hardness is 75 ppm, it's spring time, all is well. Fish are happy and your favorite plant, American pondweed, is beginning to rear its head along the shoreline. Game fish chase newly hatched baitfish and the feeders show lots of activity. Sound familiar? Spring yields to summer and your pond begins to shrink a little bit as temperatures rise. Not much rain this summer and your pond drops three feet by late August. You decide to analyze the water chemistry again. Alkalinity has moved upward to 110 and hardness has risen to 150 ppm. pH is 7.8. Your biologist says all is well, just summer doldrums and evaporation have caused your pond to shrink and its numbers to rise.
Remember, as your pond shrinks due to evaporation, all that leaves is the water. Everything dissolved in it stays behind. The concentrations of dissolved minerals and metals rise. As plant life expands and grows, biological activity changes water chemistry, too. Oxygen rises and falls, so does carbon dioxide as plants photosynthesize and respire. There are other gasses in your water, too, from the decomposition of organic matter. When you combine all these things, there's a lot going on in your water. As all these elements come together, reactions occur.
For example, here's a classic example of real world stuff. Your plants get out of control, so you decide to buy an herbicide and knock out part of the green mass. Just as the label says, you treat 1/3 of your pond. The plants die and disappear within a few days.
But, you've noticed your fish aren't feeding like they should. Then, a few days later, several of your prized creatures float to the top, belly-up. You get that sick feeling deep in your tummy.
What happened? Chances are, when those plants died, they began to decompose and alter the water chemistry. As the chemistry began to change, it affected the biology. Decomposing plants took up lots of oxygen, faster than remaining plants and the atmosphere could replace it. At the same time, pH changed, so did the amount of alkalinity, because of the gasses being given off by dead plants.
All these things combined to wreak havoc in the pond and temporarily upset its delicate balance. What finally killed the fish? They suffocated. Oxygen depletion.
But, what actually caused their ultimate demise was a combination of factors that altered a number of things dissolved in the water.
Here's another example.
I'll always remember a time in west Texas. A west Texas cotton farmer built a small pond and then filled it with his well. It sat adjacent to his house and was loaded with plenty of structure and habitat he designed. The mission that day was to stock the little pond. I'd left early in the day and made the trek near Post, Texas arriving mid-morning on that hot, early summer day. Post had been in an extended drought and it was refreshing to see a pond full of water. We got the fish stocked and then he asked me to drive a few miles to his farm and look at several smaller ponds that were seriously low due to lack of rain. We drove across the dam of the first one, stopped and got out to look closely. The pond had a yellowish tint, with a hint of green and ring of bushy pondweed around the edges. Off in the distance, a storm loomed, one of those west Texas beauties that turn the skies a deep, dark blue with some eerie green. We looked at another small pond and then headed to his barn as the wind began to whip. Safely inside the barn, we talked about his ponds as the temperature began to drop. The wind was gusting, typical of this sort of weather event and we could see columns of rain in the near distance. Then, it hit. Downdrafts of air pushed as the storm surged through. Plants danced and dodged as raindrops as big as silver dollars began splattering on the ground near us. Then, the voices of thunder rumbled louder and lightning strikes were closer. About that time a blinding light bolted fifty yards away and the crack of thunder immediately followed. In awe, we watched as this storm unleashed its fury on top of this farm. Hail as big as a baby food jar bounced like golf balls, some of it shattering like a snow cone dropped on concrete. The sounds of it hitting the barn were deafening. Heavy rains followed the hail and gusty winds. Then, just like it came, it was gone, headed to the east to offer havoc on other areas of the state. Later, I found out this storm was part of a line that extended from Mexico, through Texas and into northern Kansas, spawning more than 20 devastating tornadoes that day.
As the smell of fresh rain lingered around us and looking on the backside of that awesome storm, we continued our conversation about his ponds. Those conversations became less relevant as we made our way back toward the pond dam. Water was flowing into that water body from this storm. So was hail. It looked almost like a giant glass of tea as we stood in awe, watching what was unfolding in front of us. The hail was floating along a wash, building up like a little ice dam, then water would back up, force its way through and take the ice with it. Inside the pond, balls of ice were floating. Then, I noticed a few fish, piping for air at the surface.
What was happening?
The pond water had been warm. It was summer, after all. The pond had evaporated, so mineral and metal content was higher than normal. All of a sudden, this frog-strangling storm with way too much ice converged overhead and dumped on this little pond. Between a rapid change in water chemistry and a huge drop in temperature, the fish didn't stand much of a chance. They died from shock. And we watched it happen with no opportunity to help.
Paying attention to your water chemistry is an important part of being a good steward and thoughtful pondmeister. Understanding your water chemistry is a different story. Then, understanding what to do about it is another story altogether.
Bottom line? Knowing what water chemistry you have helps you understand what you need. At that point, the mission is to do what you can do to stabilize your water and protect it from dramatic changes. That's why biologists recommend things such as aeration, liming, fish feeding regimes and the sort.
All these different management strategies come together to help guide you to better health of your pond and its inhabitants.
Reprinted with permission from Pond Boss Magazine