Fish Story – or – Mystery Pond Detective (My thanks to Richard Strange for a hellaciously good Water Quality course!)

Pond Detective, here. It was a dark and stormy nigh…er- day, and I’d been been called pondside by a worried koi keeper. One of his fish was dead and the others were clearly distressed. His fish (who weren’t talking) had all been cleared the week before by the local Infection Police, so we both knew it wasn’t an infectious problem. Aside from alien invaders, he had a problem. My job? Detect it (Dum-da-dum-dum).

After obtaining as accurate a history as is possible, including pond cleaning, feeding, water changes, water source, filter maintenance, and testing history, I’ll quietly observe the pond and the behavior of the fish. I’ll look at the appearance of the water, at the flows for rate and direction, at the inlets to the pond and sources of aeration, and take deep sniffs of the air around the pond.
It is a quiet, kidney-shaped bare-liner pond with a small waterfall and a gentle, meandering stream. Minimal in-pond vegetation. It is edged with cobble rock; no limestone flags that I can see. I estimate its volume at about two thousand gallons with a maximum depth of 3.5 feet in the general area of the pond furthest from the falls and stream. The water has a slight green tinge, and the healthy “watermelon aroma” is absent. The 20 large koi are sluggish, and appear unhappy and clamped. They are grouped at the falls end of the pond and are not schooling. Even small noises or disturbances at the edge of the pond seem to stress them. One or two of them flash occasionally.

Hmmm. A water quality issue, eh? Well, the routine is what gets results, as my old beat sergeant used to say (before he took up surrealist bonsai). Observation complete, time for the first test.

First test: Chlorine/Chloramine. Our area relies almost entirely on the Chicago municipal water supply, obtained from Lake Michigan and depending on the season and the whims of the Water Department, heavily chlorinated. It’s a common mistake when doing water changes: a high volume change (replacement of water lost in cleaning or added during bottom cleaning with a hose-powered “vacuum”) introduced directly into the pond without aeration or use of dechlor.

Test : Real pink on Chlorine, less so on Chloramine. Preferred would have been zero (clear).

It’s also easy to fix. If there isn’t an ammonia problem, you can use sodium thiosulfate crystals or Novaqua. Amquel is a better all-round choice. I’ll warn the client that tap water needs to be treated as it goes in or his fish’s gills will look as bad as his lungs do (did I mention that he’s a two pack a day guy?) and for about the same reason.

I’m not gonna act on this one until I get more information, though. Might regret it.

Dimensional warp. Someone must have reversed the polarity of the neutron flow. Either that, or leprechauns have been doctoring my test kits with merthiolate. The area gives an existential hiccup and…

Okay. Chlorine/Chloramine negative. I guess he isn’t totally stupid. Out comes the DO meter and we do a quick read at multiple areas of the pond. A quiet pond is probably an oxygen-poor pond, and there are no air stones anywhere to be seen (our owner feels that too much water movement disturbs the oriental tranquility of the ecology, and air stones don’t look “natural”). The only air-water interfaces I see are the pond surface itself, and the smooth sheet of the gently flowing waterfall.

Test: DO 4mg/L at water temp 75 degrees at the deepest point, 5.5mg/L at the point nearest the falls and stream. We want 7.0 or better.

Restraining the urge to advise our client to take up wolverine-breeding, we send him out to purchase a competent air pump and several large air stones and hose to link them. He is also advised to upgrade his water pump to put a more vigorous flow across his falls, and to interrupt that smooth, serene sheet with a bunch of jagged rock to enhance air-water mixing. Better yet, a home-built Bakki shower hidden in the rampant trumpet vine behind his falls would work even better. Got a set of plans right here.  Serenity be damned. His fish gotta breathe!


Blerp. Another dimensional hiccup. Someone is really messing with the time stream around here. As soon as I straighten this guy’s pond out, I am going to prod some serious buttock. Might even have to get medieval on him.( Might have to go with Morris Dancing or three-field crop rotation. If he really gets me mad, it’s the Maypole for him…)

Right. Reset again. He proudly shows me the hidden bioreactor system behind the falls feed, and his DO at 75 F. is 11mg/L. Not the oxygen, then. Pretty classy system, too, and really well-hidden. Alkalinity next. A number of reasons for this. First, he’s got a very common setup as far as basic pond construction is concerned; a bare liner bottom and no source of carbonates. Second, he’s got a flashy, high-end filter system that depends on high-efficiency media in a small space. Third, he, like most koi keepers of my acquaintance, is way overstocked for the absolute volume of his pond and is relying on his space-age bioconverter to keep up with the load. I start to do the titration and he looks at me like I come from Mars. ( his kit consists of teeny-tiny tablets in impervious foil pouches. He’s never heard of Alka-whatzit and gave up trying to test his own water when he broke a tooth trying to open one of the childproof test containers.)

Alkalinity: 12 ppm Wanted: greater than 100. Preferably 140-150. Aaarrrgh. Filter crash! Need a bunch more tests: pH: 6.8 Want: 7.5

Temp: 75 F (about 24 C) (Can’t do anything about this, but it’s important)

Total Ammonia: 5.4 mg/L (Zero would have been nice!)

Unionized ammonia: 0.18 (Yeah, what he said!)

Salt: 1.88 ppt (Whew, finally something good. That’s about 1.5 lbs. 100 gallons and should take some of the stress off the fish. Better yet, I don’t have to mess with that now, and can take direct action.

Right. I’ve got 5.4 ppm ammonia in a 2000 gallon pond. I know that commercial grade amquel will take out about 1 ppm at a dose of 0.5 cc/gallon. I’m gonna need 1000cc x 5.4 ppm= 5400 cc of Amquel into this pond before I do anything else. (I also have powdered Amquel, but the conversions are a little complex, especially since what the manufacturer says it’ll do is not reflected by actual tests. It’s actually about two and a half times more potent than it claims!).

It’s been an hour. Amquel’s had a chance to work. Salicylate method Ammonia tests zero. pH has dropped to 6.6 because of the old-formula Amquel I’m trying not to waste. (The new stuff is supposed to be buffered). In goes a 5 pound box of Arm & Hammer Bicarb. Test after an hour or so and adjust the next bicarb dose to bring the alkalinity up above 125ppm, though we’ll want to go slowly from this point on to minimize stress on the fish as the pH corrects. Water changes will help too, but the salt and bicarb dosing will have to be corrected after each exchange.

The first thing we tell our client is that he may not feed his fish for a good two weeks, until he’s got some ammonia-nitrite bioconversion back, and after that only sparingly for another two weeks until his nitrite-nitrate bugs kick in. His old population checked out during the crash.

The time spent waiting for our chemical fix to work was spent giving our client a crash course in basic chemistry and biology, and then a list of suggested test kits that won’t frighten (or injure) him. Routine testing of Cl, pH, Temp, ammonia, Nitrite, DO and alkalinity on a regular schedule, and the use of salt and buffers as needed to lessen physiologic stress and stabilize pH should keep him out of trouble.

The most difficult thing to grok in this hobby is the blinkin’ awful interrelatedness of everything we do. Our fish interact with the water, the air, the filter, the feed…it goes on and on. Even after years in the hobby, we’re all still learning.

Humph. No more time glitches. Well, on to the next mystery. Pond Detective’s work is never done.