Nitrate Effects

[MikeM]

Most discussions of nitrogen in a koi pond end with the conversion of nitrite to nitrate, descibed as a relatively harmless substance. The general advice is do 10%-20% water changes per week and nitrate will never rise to harmful concentrations, or so it is said.

Well, I've been reading old Japanese magazines again. Nearly 14 years ago, Takayuki Izeki, writing on behalf of the ZNA research division, shared his observations of the effect of nitrate on the white ground of Kohaku. He urged that the maximum concentration of nitrate be 15 ppm, stating: "anything more than this and the skin gradually begins to deteriorate, improving again as the concentration lessens." He recommended that if nitrate can be kept at 5 ppm or less, "the skin becomes so white it virtually shines". He ascribed the negative effect of nitrate on (1) reduced ability to discharge metabolic toxins from the body, resulting in build up of metabolic wastes in the skin, and (2) on the pond water becoming less receptive to dissolution of atmospheric oxygen into the water. He expressed the view that nitrate levels above 10 ppm adversely affect oxygen dissolving into the water column such that saturation levels at given temperatures cannot be readily maintained.

When I raised Discus, my goal was to keep nitrate below 50 ppm at all times and try to be below 10 ppm. I considered 10 - 15 ppm to be about as close to ideal as I could get without doing daily large water changes. The battle against nitrate in the small confines of an aquarium was one of the factors that led me to give up on Discus. In my pond nitrate levels are typically around 20-25 ppm, but frequently rise to 30 - 35 ppm, and only after major water changes do I get the nitrate below 15 ppm. With the number of koi I keep I do not believe I could maintain the ideal levels suggested by Izeki without a completely different sort of filtration and maintenance regimen. The oft suggested ratio of one female koi per 1,000 gal and one male per 500 gal might make it possible for me to maintain nitrate levels in the 5 - 10 ppm range. However, I cannot imagine reducing the pond population that much. If anyone is keeping nitrate levels in their koi pond below 15ppm continually, I'd like to hear how it has been accomplished.

[JasonS]

I have no clue how I'm doing it. ... Well, I suspect the algae consumes a good deal of it but otherwise I'm just doing regular water changes and I have a bead filter followed by a shower. All winter it was just two bead filters with no shower and when I tested the nitrates 2 weeks ago it came up to about 7ppm. This was the day after I completed the stack of crates that make up my shower.

The shower is roughly equivalent in volume and throughput to a three tier Baki Shower. I just added 20Kg of Bacteria House media to it 3 days ago, so the BH media has nothing to do with the nitrate levels being around 7ppm. I'm due to test the nitrates again today but the fish have been spawning so I'm afraid of the results! ops:

I just removed about 19lbs of fish from my 6500 gallon pond yesterday too. I figure there must be about 30lbs left. The pond had about 70lbs of fish all winter -- the other 20lbs went into my goldfish pond, AKA the Q-pond, which has a different kind of algae (the short light green type) and filtration (Cloverleaf II filter fed by bottom drain and a skimmer that bypasses the filter; just added a tiny shower to the circuit 2 days ago). I don't keep good records on the Q-pond, don't recall EVER doing a nitrate test on it, but I suppose I can do that now.

What am I doing? 4 foot deep ponds, rectangular, overstocked, water changes on order of 10-30% a week (depending on season and gumption), good growth of algae on the sides. I don't think my tap water has significant nitrates. I don't think the current showers I have do anything for the nitrate levels.

I am trying to get the nitrates below 5ppm, I agree with Mr. Izeki on this goal. The whites on my fish have been very consistently good and the skin seems more related to the quality of fish that anything else for my pond. This shower filtration is expected to help with the nitrates, in addition to all of the other benefits that shower filtration is supposed to provide.

Update: main pond still at 7ppm, Q pond at 35ppm.

[MikeM]

Jason: Keeping nitrate at just 7ppm after a spawning is extremely good !! I've gotten private email from two people who maintain nitrate levels below 10ppm. One I know to have an excellent filtration system & the other described what sounded very high-end. In both cases, frequent/daily discharge of settlement, moderate stocking levels (approx 500- 600 gallons per koi) and multiple water changes weekly were standard procedures. One indicated a belief that reduced stocking levels was the reason for his low nitrate readings.

Until recently, I was at about 275 gal per koi. (Still am if counting 4 little babes being grown for fun.) Guess I need to find some more homes.

[MikeM]

And, I forgot to mention that the my correspondents' ponds do not get much in the way of leaves etc blown in.

[B.Scott]

I think there are a couple of things we need address before we can compare info regarding nirate levels.
First off the test itself. I have found that drop kits are, in general, very unreliable. Many of these will not measure any lower then 12 mg/l Last summer I tried doing 30% water changes a day. Nitrate levels in my tap water are 0.9 mg/l. On the drop test I used is was supposed to be able to measure down to 2 mg/l. I consistantly got reading around this level. However when I cross checked it findings with a Hanna tester I was running 10.7 mg/l.
It's easy enough to say I have a low reading but that is useless if we all use different kinds of test kits.
Now I notice that Nurse Bishop is reading 7mg/l with her Bakki Shower. Shiro must be doing something right.
B.Scott

[JasonS]

I suspect the AP test kits SMG and I (among many others; very common kits) use are reasonably correct. I tested my main pond this weekend, just previous to a 30% water change, and found my nitrates at ~9ppm.

However, the kit's color card only has figures for 0, 5, 10, etc. So guesswork is involved for in-between colors. My 9ppm was just a little lighter than the 10ppm color. The 7ppm color is in-between 5 and 10.

But taking any of these as accurate to anything better than +/- 1ppm isn't advised. :roll:

EDIT: The *stuff* associated with spawnings in my pond is much less than with more mature, larger, fish. My older fish are only 3-4 years old and the older ones aren't from jumbo stock so only a few are over 18 inches in length. All are less than 24 inches.

And, of course, after the 30% water change they spawned yet again. But the filtration, including significant shower type with a little bit (20Kg) of BH media, seems to be keeping things very healthy. Spawnings don't seem to effect water quality much, if at all. Excepting the visual aspect with all the foam, of course. :lol: