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I just *love* the internet, but its awfully hard to seperate the wheat from the chaff. Many ponders accumulate information which is outdated, unsound, technically incorrect, or based on old wives tales. This page is a pointed attack at some of the more common myths. You Gotta Have Plants
Plants are *nice*, plants are *good-looking*, plants may help reduce your nitrate level, but you don't absolutely need them. My pond is living proof of this. The only time my pond has plants in it is during the spring spawning frenzy where I use floaters as natural spawning mats. Healthy fish which are not subject to predation will be more "friendly" because they cannot hide. Fish which are more easily seen can also be more quickly evalutated for injury or disease. In my opinion, there are koi ponds, and there are watergardens. Ideally the two are separate entities.

Plants Will Out-Compete Algae
Nope. Wrong. Algae will out-compete plants. Scientific fact. What plants do instead is provide coverage of the surface, thereby blocking sunlight from reaching the algae. In this way, they do reduce the prevalence of algae, but the mechanism isn't via nutrient competition. In fact, nothing in your pond has anywhere near the ability of algae to grab nitrates and phosphates. Algae has been around since the dawn of time. Some strains haven't changed at all. They have stayed around because they can out-compete absolutely everything else around them. In the geologic time frame, higher plants are Johnny-come-lately's compared to algae.

A pH Fluxuation From AM to PM Is Healthy And Normal
Nope. A pH change of more than 0.3 points indicates you have either an ungodly plant/organic load, massive overstocking, insufficient oxygenation, or carbonate poor water. A proper koi pond will have a pH as solid as a rock. Koi don't like pH changes. Don't get suckered into believing a swing is somehow "normal". When I'm called-in for a pond consult, the first thing I look for aside from basic water chemistry, is such a fluxuation.

Use Vinegar To Safely Lower A Ponds pH
I encounter this all the time in rec.ponds. Vinegar is acetic acid with a concentration of 3% to 6%. Acetic acid is a very poor, very weak, complex, organic acid. It makes great salad dressing but a lousy acid. When compared to simple 2-element acids (Ie, HCl), acetic acid has only one free hydrogen to contribute for every 100-ish atoms. In contrast, hydrochloric acid has one free hydrogen per molecule when it dissociates in water. Want to hear a kicker? Acetic acid is actually toxic to fish. No kidding. To further add insult to injury, vinegar decomposes into a long list of organics, all of which must be broken-down by bacterial action. This increases the bioload on your pond, consumes oxygen, and contributes to high waterborne bacterial counts. Vinegar in solution is an eye and gill irritant as well. With all these problems, you wonder why people continue to use it.
Note: I once did a math comparison between HCl and Vinegar. Did you know it would take over two *gallons* of evil-smelling vinegar to equal the acidification power of 50 cc's of HCl?.

Baking Soda Will Drive My pH Up To Over 9.5
Nope. Actually, it will peg it at a rock-solid 8.4. You can completely saturate a water sample with baking soda and never see a pH higher than 8.4. Baking soda is a strong buffer, and very useful as a water additive in carbonate-poor areas. In a properly buffered pond, the dreaded pH "crash" is an impossibility. Maintain your carbonate hardness (KH) in the 100 to 120 ppm range and you can forget about "crashes". Besides being universally available, safe to handle, non-toxic to children, baking soda is harmless to fish at any reasonable level (ie, < 500 ppm).
This interesting artifact is highly useful in testing the performance of your pH test kit. Make yourself a cheap and very reliable pH 8.4 reference solution by dissolving four teaspoons of baking soda in a cup of distilled water. The resulting 8.4 pH solution will show you how much (if any) your test kit has wandered.

Muriatic Acid Is Highly Toxic To Fish
Nope. Muriatic acid (aka hydrochloric acid, hydrogen chloride, "Pool acid") is *harmless* to koi and goldfish when used responsibly. In fact, HCl is the correct tool for the job if you live in a hard-water area (like me!). Very little HCl is needed, it is non-toxic when dispersed in water, does not introduce food for bacteria, and is *dirt* cheap. See the discussion on Reducing Carbonate Hardness before using it however. Like any strong acid, it can drop the floor right out of KH figure right in a big hurry. But note this isn't "toxicity". Far from it. Any acidic compound will do this. HCL just excels at it far above what would seem to be a "normal" level. Lacking any carbonate buffers, adding HCl *will* produce a pH crash and this *will* kill fish. Acid is a tool. Use it wisely.

All This Technology Is Needless. My Pond Is 100% Natural
Your pond *might* be a natural pond... if it can pass the following test: Turn off all UV, pumps, filters, etc. Close all inlet and outlet valves. Stop adding water. Stop feeding the fish. Now walk away and leave it to fend for itself. Return in a month and make the following super-scientific observation: Are there dead bodies everywhere? Does it look like a toxic waste dump? If so, you've just shot that theory all to hell. The moment we add more than a couple of fish for every (wild guess here) 50,000 gallons, we no longer have a "natural" pond. It simply can not sustain itself. Natural ponds take care of themselves. We on the other hand must resort to all manner of artifical support methods including pumps, biofilters, UV lights and a host of super-engineered feeds and medications. So lets not kid ourselves here. Most ponds created by man (99.9%) are in no way "natural". So lets further agree that we won't bash the notion of adding "evil chemicals" and other such "un-natural" support mechanisms to the pond. All these "awful" things are simply tools. Learn about them, use them wisely, and don't sweat the "unnatural" label. Say it with me folks: "I have an unnatural pond".

A UV Light Can Over-Sterilize My Pond And Cause Immune Dysfunction
Nope. If you don't believe me, crank-up your UV light for several weeks and then take a random water sample and put it under a microscope. Billions of critters wandering everywhere? You betcha. So much for the oft-toted "sterilization" effects. UV's are primarily algae-control devices with a small effect on primary pathogens. Even if they could "sterilize" the water, it wouldn't matter one bit to the fish. Understand that very few pathogens are exclusively water-borne. Most attach themselves to the skin, gills or gut of the fish where they are completely safe from UV radiation. The immune system gets a constant work-out, UV or not.

You Cant Use A Diatomaceous Earth Filter In A Koi Pond
I recently attended a lecture given by a self-proclaimed pond "guru" and heard this gem. This goofball dressed himself up in a white lab coat and cited numerous "mineral and electrolyte removal" effects. Balls... D.E filters work just fine, and no, they don't affect minerals or electrolytes! Any first-year chemistry student would giggle into his apron at such a claim. (For the record you'd need something along the lines of a molecular sieve to grab dissolved minerals and electrolytes... not something so incredibly coarse as D.E media). In fact, if you want absolutely the clearest water imaginable, you might want to look into one of these. Now for the bad news. They are a huge maintainence item. They simply work too darned well. Initially, expect they will load-up solid within 2-3 hours. When this happens you must manually back-flush them, replenish the gooped-up D.E media, etc. Lather, rinse, repeat. You can count on doing this daily until Hell freezes over. But you'll have some amazingly clear water. Is this filter system for you? Likely not... but it *can* be used with koi. I've done it.

Koi Hibernate During The Winter
Koi do not hibernate. They get cold, they get miserable, they sulk near the bottom of the pond where it is a trifle warmer and try to think happy thoughts. If they had opposable thumbs, they'd be knitting booties... but they do NOT hibernate. This is one of those wierd defense systems which evolved a bit differently than classic hibernation in other animals. Koi are still very much aware of their environment even in 33F water. They are simply "powered down" a goodly bit to conserve energy and weather the winter while using as few calories as possible. If you disturb a koi which is in "winter-mode", he'll move away from the threat in a few seconds. Sluggishly, but he'll move. An animal in true hibernation would take lots of stimulus before making any such response. Many animals would actually be unable to move at all.

Never Feed Your Koi When The Water Is Under 55 Degrees
True and false. This really depends on where you are geographically. In most areas where the pond will get very cold (ie, under 45 degrees) or freeze-over completely, this is indeed very solid advice. There are some real problems with food rotting in the gut at cold temps. A problem unique to some areas however has to do with a very temperate climate where the winter water temperatures hover around the low 50's. Under these conditions, koi are at risk for both starvation and parasite attacks. If you live in such an area, you may indeed continue feeding. Rather than feeding nutritionally- transparent foods like Cheerios, feed small portions of medicated foods once or twice a week. Under 55 degrees, the koi immune system becomes rapidly attenuated. Until the water temperature drops into the mid-40's however, many parasites and disease processes can remain active. So the idea is to give your fish enough dietary support that they neither gain or lose weight and are able to make the best of a compromised immune system. The use of a medicated food (Romet B) is precautionary. Under these conditions, oral meds are generally well-absorbed due to the extended contact time in the gut.

Koi Ponds Need To Be At Least (X) Feet Deep
This statement is part myth and part truth. Ideally, koi ponds would be 30 feet deep, 120 acres square, have a pH of 7.8, temperature of 76 degrees, a carbonate hardness of 120 ppm, elemental calcium levels of 180 ppm, would have underwater speakers playing Pink Floyd, maintain a constant sun angle, and would be fed with an endless supply of antarctic krill, green veggies, etc. Well, guess what? It isn't gonna happen, folks. The real truth is, koi can be kept in water less than 1 foot deep... if all the other water conditions and chemistry are right. You won't see maximum growth, you won't get great body lines, and you sure as heck won't breed any show winners, but you *can* keep koi in shallow water. The Japanese have done it for years. Now, having said that, what exactly can we consider a "nominal" depth? I like to see at least 8 inches of water under the fish when he stands on his tail. If you have 24 inch koi, you'll need at least 32 inches of water. This number isn't cast in stone, but its a reasonable rule of thumb. More depth is certainly better, less depth is much worse, but people can and *do* use this formula successfully.

Concrete Is Toxic To Fish
If you change this to read "large amounts of fresh, unleached concrete can kill fish due to alkalosis (high-pH)", then you would be correct. Concrete is harmless to fish once it has been leached. How do you leach it? After the concete has cured (30 days), fill the pond with water and add muriatic acid ("pool acid") to drop the pH into the upper 4's or low 5's. Keep adding acid to the water to maintain a very low pH. If you have a submersible pump which has no exposed metal parts or metal shaft seals, throw it in to circulate the water. Be aware that fresh concrete can soak-up a remarkable amount of acid. Keep dosing acid up for 5 days. Now let the pond sit and monitor the pH. If it starts jumping in the upward direction, hit it with more acid for another few days. If it looks fairly stable (ie, it stays under 6 for more than 24 hours) you are done. Drain the pond, scrub the walls with a stiff broom, hose-off the chalky white residue, and refill. Add declor, maybe a bit of baking soda if you have carbonate-poor water and you are done. The pH will still creep-up a bit for the first few years, but this will happen very slowly. Concrete by its nature will continue this trend for many, many years. To combat this, add a bit of acid followed by baking soda sufficient to drop the pH if it gets much over 8.6. The acid drops the pH while the baking soda helps to *stabilize* it somewhere between 8.0 and 8.4.

It's Unsafe To Run A Pump Over 2/3rd's Of Its Rated Output
This is sheer engineering idiocy which isn't supported by basic electrical or mechanical engineering.... or the pump manufacturers themselves. This little tidbit of internet folklore got started by a previously-unrecognized Canadian genius!

Reproduced with kind permission from