A couple of ORP questions??

[cmungo]

Quote: Originally Posted by JasPR yes, a trend downward in ORP observed at the same time of day means the oxidative potential ( oxidative 'reserve' really) of your water is dropping. Organics would be the number one reason, increased bacteria behavior and loss of oxygen would be the next. And acids building in the water and resulting alkaline reserve exhaustion/pH slipping would be the third reason. But the real benefit of high ORP is a conformation that your system is designed well, in balance and not overstocked. If you chart your decline in ORP with water change schedule you will get a good sense of how far you move from ideal base line readings between those water changes. The same can be done with alkaline reserve and nitrate readings. JR

What nitrate ppm (or change in ppm) would it take to effect the orp reading?

[farne230]

JR, is it true measuring orp is a slippery slope say you take readings for one week (200 to 300) then you calibrate, reading drop 120 to 200, then you check again and differant again... the act of calibration and stability of equipment is in question I suspect, and you begin to question the results, is this true??

[JasPR]

Honestly, that I don't know. What I was describing was an environment where water is deteriorating in a closed system. Pollutants building and alkaline reserve declining as the pond system moves progressively towards eutrophication. This accumulation of nitrogenous wastes in the form of both gaseous and non gases species represents a shifting in bacteria species and counts. The sum total of all reductive and oxidation reactions increases and shifts towards a more reductive environment.
As you may be aware, in the very demanding hobbies of marine keeping and reef keeping nitrate levels need to be below 10 and in many cases, it is better to get unreadable micro levels of nitrate. In a koi pond, that is not realistic and we tend to use 50 as a line in the sand.
I tend to do a lot of water changes ( two a week) and dump sumps daily. So I have a low nitrate reading- typically lower than 10. But my ORP has never been as high as 400 mV because even though I am always at oxygen saturation levels for temperature I run only a slightly alkaline pH at 7.4 and use soft water with a relatively 'hair raising' alkaline reserve of 70-90.
I do use baking soda- only when I'm making pastries however.

I do 'borrow' Thiel's R factor ( rH2) , which he borrowed from the German marine hobbyists in the 1970s. In such a formula, you double the pH # ( in my case that's 7.4 X2= 14.8) and then add that to the ORP reading after dividing that by the constant of 29. so my ORP of 380 divided by 29 = 13.10
Adding this to the 14.8 ( the pH X2) and I get a value of 27.9. This value is consistantly lower than Thiel’s or the German’s definition of highly oxidative water due to the fact that marine system water is of a higher pH typically in the low-mid 8's. This is also way rH2 is not the whole story or a good picture for eutrophic systems like koi ponds. And a living example as to why adjusting pH to accommodate higher rH2 factors is not the point of the exercise.
So we add in the factors of temperature and dissolved oxygen. Now we are getting a more real world view of ORP as a measurement in a living system where biomass and decay change oxygen values. And also we are more accurately reflecting a living system designed for the parameters that koi are acclimated to historically. This is where I adopted the pond factor as opposed to Thiel’s marine calculation.
Now we redo the math:
380 ORP divided by the constant of 29 = 13.103
Plus the doubling of pH ( 7.4 X 2) = 14.8 + 13.103 = 27.903
Now include this as an example: 69.5-70 F will give a dissolved oxygen reading of 8.975
Adding this dissolved oxygen # to 27.903 = 36.878 ( 35 plus being the ideal of target #)
I then constructed the tables around these final values. What you find is that at very high temperatures, where dissolved oxygen falls off tremendously ( at 95 F we see DO at 7) we see this number fall to 34.90. This corresponds to a 70 F pond with an ORP of 322 mV.
So within the band of ideal parameters for nishikigoi: pH of 7.2- 7.8 and within the ideal metabolic temperature range for koi 68- 76 F, I created a cross reference chart in which ORP values are above the minimum oxidative values.
JR

[PapaBear]

I don't want to take anything away from the learning from JR and MCA, but I wanted to toss this into the mix concerning your source water.
If I remember correctly you moved across town last year and your water parameters changed drastically with ph, kh, gh, all going down considerably. I may be thinking of someone else, but I thought it was you anyway.
The likelihood that you had moved to an area further away from the water treatment facilities was opined (by me) or the possibility that your source water was from a different aquifer or lake requiring different treatment than you had on the other side of town.
The reason I bring this up is the ORP readings and MCA's comments on it's relatively low level as potable water sources generally go. I would be very interested to see a complete water test regime on your tap water, including Chlorine/Chloramine, Nitrate, Ph, Kh, Gh, TDS, Trihalomethane, Haloacetic Acid, Bromate, and Chlorite. If your water treatment plant is a great distance from your home it is possible that organics are degrading the Chlorine/Chloramines in the water mains and producing any one or two of the last four compounds on my list. That might help to explain your low tap ORP. If biological action is taking place in the municipal water mains it would also explain the reduction in Kh and Ph relative to your former home, as carbonates would be exhausted in the process.


JR,
What influence in the pond setting would the addition of supplemental carbonates from BS, Oyster Shell, etc... have on the ORP numbers. Folks like Brutucz with such low KH numbers pretty much have to supplement with something if they have much of a fish load.

[MCA]

Remember the koi keeping season is 24/7....it starts when the koi hit the water.

Koi produce waste (ammonia, urine, feces) 24/7...just in varying amounts.

[JasPR]

JR, is it true measuring orp is a slippery slope say you take readings for one week (200 to 300) then you calibrate, reading drop 120 to 200, then you check again and differant again... the act of calibration and stability of equipment is in question I suspect, and you begin to question the results, is this true??

ORP is a tricky reading and odd trends should be considered suspect. What an ORP meter can do is gove direction and trend if you read it the same time each day and in the same area of the pond. But the units themselves are very easily fouled, especially by oxygen molecules and biofilm building on a probe. And the probe itself must be the correct electrodes and be using the right internal calibration for the pond setting. So a LOT can go wrong with your probe that makes odd readings moot. Most common is a drifting reaction. This is common where oxygen bubble form in the pond or near the algae covered pond walls. I have my units in the filter and that means they need to be cleaned regularly. I use two meters/probes so that one confirms the reading of the other.
If you have active algae ( green water), an ORP meter will be whipped around just as your pH will be and your DO levels will be. If you measure them all you will see the trend lines clearly. I've seen green water shoot pH up into the high 9s and then down to the low 8s. That is a huge move and the ORP will follow.
ORP is perhaps the most unreliable of all measured parameters. But it is terrific for assessing a ponds operating ability, pollution trend and appropriate stocking levels.

[MCA]

Quote: But it is terrific for assessing a ponds operating ability, pollution trend and appropriate stocking levels.

And for double checking any PP dose calculation for parasite treatments. No one can guess the ORP level from the shade of purple.