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/Aquatic Gardens, Design, Construction & Maintenance

Water Quality for Aquatic Gardeners


By Bob Fenner

Aquatic Gardens

Ponds, Streams, Waterfalls & Fountains:
Volume 1. Design & Construction
Volume 2. Maintenance, Stocking, Examples

V. 1 Print and eBook on Amazon
V. 2 Print and eBook on Amazon

by Robert (Bob) Fenner

"Yes, Boris, accompany me in the La-bore-ah-tor-ee"; is this what comes to mind, along with a fiendish laugh, when you think of water chemistry? Well, you won't have to put on a white lab coat, or dust off your ancient slide-rule to be a successful waterscaper. Follow along with me here as we introduce the basics of water chemistry, the what and why of water for the uninitiated.

In the following Section we'll delve into the nuts and bolts of test gear, with super-easy explanations of the "how" and possible treatments to manage your water. Finally let's cover the understanding and prevention of our arch-rival and friend, the algae.

Parameters To Be Aware Of:

If you were so inclined there are several chemical components and physical properties of your water that could be measured and manipulated to achieve "optimal" results. Happily, there are only a few simple parameters that an earnest aquatic gardener needs to be aware of; temperature, pH-alkaline/acid reserve, and some aspects of nutrient/waste concentration called the nitrogen cycle. Additionally, you will want to be able to measure your gallonage and for anything you're adding to the water.

Poisoned or No?:

If you're looking for a murder mystery, or the A, B, C's of how to do away with your spouse, keep searching. Here I'm asking you if your aquatic system has life in it or not. If it's abiological (nothing living in it) this is the area for you; if not, skip on down to the next heading.

Poisoned systems are ponds, fountains, falls that are intentionally kept without life. There are several modes, selective and general to keep them clean and clear. For our purposes here we'll describe the three most popular, doing nothing, copper-based, and pool/spa technology.

Doing Nothing:

Just filling the system and letting nature takes it's course is generally a poor idea. Besides the algae and other mystery life that "appears" from nowhere being noisome, it can get out of hand clogging your pump, and creating a smelly, slimy, bothersome insect-breeding cesspool. If you intend to "do nothing" chemically to treat your system, you are well advised to at least install some Mosquitofish to eliminate disease-carrying vectors.

Copper-Based Treatments:

These are so advantageous in both poisoned and biological systems with fish and/or plants, that we'll devote an entire Section to their description.  Copper, the chemical element, combined with "chelating-agents" is a wonderfully safe and effective way to combat algae and pests. Additionally, unlike swimming pool technologies, copper is virtually non-toxic to surrounding landscape and inquisitive animals.

Swimming Pool/Spa Technology

Remember those days of green hair, red eyes and rainbow vision? They're not gone yet! The same sanitizers, stabilizers, defoamers, buffering agents, et al. may be used in a poisoned water feature. The same precautions apply here as for your spa or pool; you'll want to check on pH, alkaline/acidity reserve and pay attention to using the proper amounts of chemicals. Abuse will damage the basins, rockwork, pump, and maybe you.

The commonest pool sanitizers are the chlorine and bromine sticks, tablets, granules and liquids that are general biocides. The name of the game with them is maintaining a "free" ion concentration of 1-2 ppm at about pH seven. This is a lot easier than it sounds, with the use of conditioner.

The conditioner compound, cyanuric acid is a great innovation. By applying it just once (unless you change water) it will help to "hold" the sanitizer (chlorine, bromine) in solution far longer.

In actual practice, the clean water is tested for pH and alkaline/acid reserve (with test kits detailed in the next Section), and adjusted with stock acidic or basic materials (generally Muriatic, sodium carbonate aka soda ash). Conditioner is measured out per the gallonage (see below) and pre-dissolved in warm water.

Once a week in the warmest months to every few weeks/months in the coldest, you test the water for "free" sanitizer, adjust for pH and... that's it.

For Living Systems:

Having life in your water effect, plants and/or fish makes it easier in some ways and harder in others to keep "clean". Let me explain. In poisoned systems you can chemically "drive" the water arbitrarily, but must remain vigilant against invading life forms. Yes, "nature abhors a vacuum" is not an empty cliché©; algae, bugs, other life forms will start and proliferate in your water unless you purposely keep them out.

Living systems on the other hand are more like sailboats than motor-cruisers; they're steered "with the wind" in the direction of favoring the life you want. Instead of the poisoned system perspective of "fighting" the water, minerals and light, you use them to your advantage, understanding how your plants and fishes change and in turn are changed by water chemistry.


Being "cold-blooded" aquatic garden life is more or less active metabolically depending on their water's temperature. A practical rule of thumb is the Q10 factor which states that for every change of 10 degrees C, metabolic rate is doubled or halved (depending on which direction, up or down the temperature is going). The range of thermal tolerance that aquatic life displays is very wide; for many organisms, from near-freezing to almost tropical. What they cannot tolerate is rapid changes. You should do your best to build and operate your system to optimize insulation.

A great deal can be known from using a thermometer; some of the world's most successful fisherman call it their number one tool. Fish will not "take a hook" if the water is too warm or cold, and especially if the basin is deep and still enough to be thermally stratified, beneath the thermocline. A thermocline is an area of rapidly changing temperature that is due cooler, more dense water sinking, settling under lighter, warmer water. Thermal stratification is rarely a concern in small water gardens except in areas with freezing weather. Here, ponderers should take care to either not disturb their ponds while iced-over, or to continuously do so to keep them thermally homogeneous.

Alkalinity/Acidity & pH

Water is not just H2O; there are a host of other chemicals and living processes that compete to make the pH more basic (higher than neutral or 7.0), or more acidic (lower than 7.0). The absolute measure of pH is a measure of Hydrogen ion concentration. For aquatic gardeners, a much more important, related value is the buffering capacity, or alkaline/acid reserve...

Please try to understand my point of view and concern in writing about these matters. If and when you measure your waters pH you will find that it can/does fluctuate a great deal during the course of even one day. Should you be alarmed? Perhaps "do something" like a massive water change, or add chemicals? No, most likely not. Much heart-ache and loss of aquatic life is brought about by such over-reacting.

Instead, you should be aware of your water's capacity to resist such changes, aka buffering, by use of an alkalinity/acidity test kit. Such tools should always be used in conjunction with a pH measure. Ideally, by utilizing alkaline material in your filter, through water changes, or if your water source has little alkaline reserve, by adding soda ash (carbonate), you can reduce diurnal pH shift to less than one half point. (James, we should illustrate these phenomena with diagrammatic boxes showing the same starting pH point, one with, the other w/o adequate buffering... and a typical day pH shift from photosynthesis, respiration.... Is any of this clear? ARGHHHHH!)

Measures of Metabolic Activity; The Nitrogen Cycle:

The plants, fishes, algae and microbial components of the substrate and water all impart changes to your system's water. Whether you're conscious of it, or try to improve on it, or not, there are multifarious reactions that take place to convert, "cycle", otherwise off-set the accumulation and toxicity of these waste and by-products.

Most celebratedly in the pond-hobby literature you'll see aspects of the element nitrogen (N) and it's cycling. What makes nitrogen such a spiffy tool for keeping your eye on your system's water quality? Imagine being able to make an easy measure/test for what's going on in your system metabolically. Nitrogen compound testing gives you that.

Basically, all living things are made up of molecular building blocks called Amino Acids (AA for short). These are structures of carbon chains (some with sulfur), oxygen, hydrogen that are linked to one another by amino bonds to form proteins. Amino bond sounds a lot like ammonia, because it is. The nitrogen cycle is the sum total of processes that convert atmospheric nitrogen (N2) into compounds useful to animals and plants (proteins made up of AA's), that eventually make their way back (cycle) to their original start (atmospheric nitrogen).

Protein Nitrogen enters into the system mainly as livestock and food. Eaten and not most of this material is broken down/converted to (unionized) ammonia (NH3) and (ionized) ammonium (NH4) a less toxic form. Nitrification occurs principally through bacteria (e.g. Nitrosomonas) metabolizing ammonia to nitrites (NO2-) and other groups (e.g. Nitrobacter) in turn converting nitrites to nitrates (NO3-). Let's look at this in another way (refer to Figure #?); an "idealized" time line for establishing nitrogen cycling in a new aquatic garden (from CMA):

At mark "0" you've just set up your system and placed all new (read that as sterile) tap/source water. In most cases, the waterscaper will shortly thereafter ("1") introduce either A) a few hardy (nitrogenous waste resistant) fish or plants to help "pop" the system, B) A chemical "feeding" system (source of ammonia, etc. with or without a source of beneficial microbes, C) And/or some "food" as a source of decomposing ammonia to instigate bacterial immobilization.

At point "2" enough ammonia is being converted by bacteria that have been intentionally or accidentally introduced to the system to detect the presence of the nitrification product, nitrite. Point "3" denotes the beginning of Nitrobacter activity with "4" marking the detectable initialization of conversion of nitrites to nitrates. At "5" ammonia concentration has "peaked" and generally declines rapidly. Point "6" shows the same for nitrite. Both ammonia and nitrites are toxic at low levels to most fishes and invertebrates. At the time of "7", generally four to eight weeks into the set-up, both have fallen to acceptably low concentrations to allow further stocking.

Nitrates in our example continue to rise and might build to dangerous levels in a truly closed system (shown by the ascending curve of "9"). Intervention methods by biological pond keepers; frequent partial water changes, biological cycling in their filters, algal growth, abundant, vigorous live plants can be brought into play to successfully limit the "bottle-neck" accumulation of nitrate ("8").

Expediency and Rates of Reaction:

Depending on such factors as the physical format of food/wastes provided, temperature, bacteria population dynamics, and oxygen supply, biological filtration in your system can be a forgotten breeze or an unending nightmare. See Section C) ii) and subsequent on Filtration.

Allow me to elaborate briefly on these points; it's important to understanding, indeed, avoiding the most common pitfalls of live-pond keeping: metabolite poisoning.

"Here we go again"; this time it's me, not Ronald Reagan. Don't overfeed; especially dried foods in cold weather. Why? your livestock won't be able to find and process it all. In fact, the extra ammonia might overwhelm your microbes and your macro-life, either necessitating a minor/major re-establishment of nutrient cycling, or turning the whole system into an algal cesspool.

What could you say about microbiological population dynamics? They are vigorous and dynamic. Even chemical self-feeders (chemo-autotrophs if you're going on Jeopardy) like the bacteria we want have to look out for competitors, predators, lack of oxygen, too much carbon dioxide, and other sources of poisoning like fish medications. As I've written before Cleanliness is not sterility. Cleaning, vacuuming, changing water, too much, too soon disrupts/destroys needed bacterial cultures. Don't be too fastidious about cleaning all your system at once; you want good, strong beneficial microbe populations living in and on the "hard" surfaces in your water garden.

Wherefore Art Thou, Beneficial Microbes?

So it can be seen that one measure of a system's viability, it's capacity to support fish and other life, is the presence, abundance and vitality of "magical" "mystery" microbes. Well, actually, these bacteria are to be found most everywhere; in fact, they will "fall" into your system from the air, and in and on your livestock, without purposefully introducing them.

Because these bacteria are so necessary, filters are specifically designed for the primary benefit of keeping these beneficial microbes healthy and metabolically active. But what can you do to bring them on-board faster? A lot.

There are stock inoculations of bacteria cultures for sale in spades for the purpose of initially establishing biological cycling. Sometimes they work; too often they don't. The reasons for this are many. Most cultures are feeble, too dilute, and/or made up of inappropriate species of microbes. Way too many times, the hobbyist is to blame. They put the "bugs" in a chemically hostile, non-nutritive medium; or alternatively over-poison the water with an ammonia feeding stock. Watch out for these chemical solutions to "feed" your system; read and follow the directions provided to the "T"; the ammonia provided is concentrated.

If you don't want to play "mad-scientist" adding commercially prepared cultures, you can just wait to introduce much livestock for one or two months; but that there are other safer, faster and inexpensive methods. What I'm hinting at is simply transplanting the beneficial microbes from an established system to the new one. In actual practice, some of a stabilized, pollutant and parasite free source's gravel, plants, filter media is carefully placed in a sterile new-one of close temperature, and pH. Voila! Instant bacteria benefits. A "conditioning period" of time with careful feeding, testing and sparse livestock population must still be observed of course.

How Do It Know?

How can you tell how much ammonia, nitrite, nitrate you have, and why should you care? The easy answers are A) test kits and B) because at sufficient concentrations they're deadly to your livestock. Do you really need to be aware of and measure for these parameters in order to be successful? No; you're system will "cycle" either way. But a conscientious water gardener will be conscious of what is going on in there system, and understand the basics of why it's so.

Some Ideal Water Quality Measures:

Some water chemistry parameters you want to keep in mind and maintain your system at:

1) Ammonia, less than 0.25 ppm.

3) Nitrite (NO22-), less than 0.1 ppm as nitrite ion.

4) Nitrate (NO3-), less than 50 ppm.

(there is no clear dividing line in which nitrate is absolutely harmful; conditioned fishes and plants have been cultured in water of several hundred (even thousands) ppm. All that can be agreed is less is better.)

5) pH, within a range of 6.5 to 7.5 ideally.

6) Temperature, 33-80 degrees Fahrenheit. (Periodically higher, not generally a problem. Stability more important than any given point.)

What About Hardness, Phosphate, Dissolved Oxygen, RedOx...?:

I can almost hear the eyebrows of science types rising up in disapproval; "Where are the formulas (formulae?), balanced chemical reactions, biochemical pathways..." Yes, Dear Reader, outside the scope and intent of this book, there is no apparent end of further tests and interactive considerations. I could "talk the talk" further and in more detail, but why? This introduction is complete enough for ninety nine percent of people in ninety nine percent plus situations. That's good enough for me.

Should you be interested in delving into the chemistry and ph...

Aquatic Gardens

Ponds, Streams, Waterfalls & Fountains:
Volume 1. Design & Construction
Volume 2. Maintenance, Stocking, Examples

V. 1 Print and eBook on Amazon
V. 2 Print and eBook on Amazon

by Robert (Bob) Fenner
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