Sit back, get yourself comfortable, a science lesson is on the way!!!! LOL
Over to yous Prof.
"Horton"

You should test for Kh which is the buffering capability of the water. It slows down changes in PH so the fish can adapt to a change.
You should test for nitrites and nitrates. These are organic remains from rotting food, poop and other decomposing debris. The product of these will be ammonia.
PH of 6 is probably too low for koi to be healthy.
If the Ph is out of whack, it will be on the acid side most likely. The cures most often recommended on this forum are Bicarbonate of soda and Plaster of Paris which is calcium carbonate.The first will raise the PH fairly fast and should be added in small amounts over a period of time with a new test after each addition. A cup or two of bicarb in the pond in advance of a heavy rain is sometimes suggested.
Plaster of Paris or POP has a chemical reaction with acid water. It is slower. The reaction is the same as between limestone and acidic water. The chemical reaction continues until the PH is somewhere around 8. Right now I don't remember the number but that point gives you a PH that is good for the fish, won't hurt the plants (although you may need to add a bit of Ironite because the higher PH will bind up the nitrogen in fertilizer)and won't make the skin on your hands crack. I put a slug or mold of POP in the water at all times. For some reason I haven't figured out yet, murky water becomes clearer, too.
There are other ways to get rid of ammonia although a water change is the quickest. The first is aeration. Those bubblers and fountains add oxygen to the water and exposes the ammonia to the air. It has a chemical reaction with the ammonia which reduces it. A rock called Zeolite can be placed in the water flow and it will suck up the ammonia.It wears out though and must be replaced. Activated Charcoal will also remove some ammonia. It wears out too.
Barley straw or the break down of barley straw is supposed to eliminate algae as it produces Hydrogen Peroxide as it breaks down. This is primarily for string algae. Some studies are rejecting early studies for effectiveness.
Activated Charcoal removes toxins and discoloration from the water. You want the most surface area possible to be exposed and it should be placed in a bag or other container directly in the water flow .
I avoid the concoctions on the shelves of pet or pond stores as much as possible. They are over priced and less effective than the cures above. I'm sure some one will disagree. LOL! Sandy

Oops, sorry about that. David's answers will be far more elegant than mine. Sandy

Horton, you tickle me.
Thanks, Sandy. You did a good job explaining it very well. The important thing is that it answered the questions I had.
One thing about these two words, nitrites and nitrates. Why do they have to be so darn similar? I think to myself, "Ok, that's the 'A' one and that's the 'I' one." LOL. Thank you both.

Sandy, my answers...elegant??? You HAVE GOT TO BE KIDDING! I think we should let Horton answer all the chemistry stuff; he'd probably do better at that than I would with GFI's LOL!

I apologize beforehand about the length of this post but there are many questions raised. Here are links to two jpegs that you may wish to either print out to have on hand or open them in an adjacent tab/window. I decided not to embed them in this post so I dont screw up the size/width, etc. as I did in another one! LOL!

So let's start the dialogue: KH, or alkalinity, is a measure of the buffering capacity but in a special way. It only measures the ability of the water to resist a downward change in pH. Folks typically talk about buffering and buffer intensity meaning resistance in both directions (pH-wise) and then include alkalinity in the same sentence. Yes, they are related concepts but not quite the same thing. The more alkalinity you have the more resistance you will have to a pH crash. A "crash" or sudden drop in pH can occur due to sudden input of something such as a large rainfall event (pH of rainwater typically will be in the range of 5-6 but fortunately is not strongly buffered). You can increase the buffering by adding "something" that will provide either carbonate ions or bicarbonate ions (there will be a "metal" attached to them, most likely sodium or calcium or possibly potassium or even magnesium). If your pH is around 6.5 or 7 and your alkalinity is low you would want to add "something" to your water to get it into a reasonable range - I prefer to have my alkalinity in the range of 80-100 mg/L (approx. 6 drops if you're using a liquid KH test kit as opposed to test strips which tend not to be that accurate). While some folks will try to hit 150-200 mg/L such alkalinity values are inherently unstable - which I will explain later. Sodium bicarbonate, baking soda - NOT baking powder! - is the easiest form to use to increase alkalinity. Initially you add a small amount - 1/4 cup or so dissolved in pond water. Add it around your pond. After an hour or so check your pH. If your system has low alkalinity and low-ish pH you'll see that the pH has increased a bit. Keep doing this, as Sandy has suggested, but I'll add a caveat: once you reach a pH of 8.3 - which you will - you can then add as much sodium bicarbonate as you wish since it will NO LONGER impact on pH, it will only increase the alkalinity. Adding a bunch of alkalinity will have no noticeable effect on the fish since at this point your pH will be 8.3; itÂs similar in effect (on the fish and plants) to adding salt to your pond but in this case you will be increasing the alkalinity.

Using sources of calcium carbonate will also help in adjusting your alkalinity. Such sources are crushed oyster shells, crushed limestone (the "crushed" aspect provides more surface area to help it dissolve faster). Agricultural lime as sold in the farm stores isn't a particularly good thing since it also contains a high value of magnesium compounds. NEVER use what is referred to as "Quick Lime" - it is not calcium carbonate but rather calcium hydroxide. Plaster of Paris - POP - can be used but here you also have to be careful in that there are several different varieties of POP out there, many of which are based on silicate chemistry rather than carbonate chemistry (and the contents list on the bag usually doesn't tell you which) but you can test it with a bit of vinegar to see if it foams (if it does then it has some carbonates present). My preference is to use baking soda since my pH is sitting right around 8.3 so I can add it whenever with no impact on the fish or plants; the chemistry is very clear as to what is there and no worries about what isn't spelled out. When I know there is going to be a large rain event - for example, when Horton shoves some of his wonderful 40 °F weather with lots of acid rain our way I will add a cup or so of sodium bicarbonate to eliminate any impact which might occur to our pond.

If you look at Figure 1, when you add alkalinity you are shifting the WHOLE CURVE to the right. The SHAPE of the curve will remain the same. By increasing the alkalinity you have minimized the possibility of having your pond pH crash since it must attempt to change the pH from about 8.3 down through 7.0.....notice that somewhat flat plateau around point B? This moves to the right as you add alkalinity and therefore it would take more and more hydrogen ions to reach that point, i.e., it becomes more buffered. But also take a look at Figure 2. Many gases dissolve in water: carbon dioxide, oxygen, ammonia - to name a few. When carbon dioxide dissolves in water it forms dissolved carbon dioxide (and carbonic acid), bicarbonate ion and carbonate ion although not much of the latter for the pHÂs we encounter in our ponds. WhatÂs important at this point is that the solubility limit for carbon dioxide is approximately 0.5 mg/L - the top curve - based on the average carbon dioxide levels in the air. In cities where CO2 levels may be a bit higher then the solubility levels will be slightly higher. This solubility limit is set by the amount of the CO2 in the air and the temperature - predominately. It is essentially independent of pH, or whether or not you aerate your pond. Using Figure 2 letÂs assume you have a pH of 8.3 and an alkalinity of 80 mg/L. This also means that you have a dissolved carbon dioxide/carbonic acid of approximately 1 mg/L (the second line in) or twice what the amount of CO2 that would be in there if it were just in equilibrium with the atmosphere. The result is that your water is super-saturated with respect to CO2 and therefore CO2 comes out of solution and at the same time reducing your alkalinity over a period of time. In our culture "more is better", or so weÂve been led to believe! - so letÂs increase the alkalinity to 200 mg/L. Now the CO2 is FOUR times above saturation. The result is that this represents a very large driving force to push CO2 out of solution (the rate at which it comes out of solution is exponentially related to the amount of CO2 in solution). This is what I meant by high alkalinity values being inherently unstable; it protects you better against the potential pH crash (dropping below 7) but wonÂt do too much for the usual diurnal or daily pH swings. The second aspect of pH variability in your pond is usually the result of algae. During the day algae produces oxygen sometimes to such an extent that you will see some forms of algae actually float to the surface (disturb the mat and fine bubbles are released). The use of CO2 during photosynthesis results in the pH rising sometimes as high as 9.0 or even slightly higher. During the night - no sunlight - the algae respire or produce CO2 rather than use it with the result that by early morning the pH has dropped significantly. If you look at Figure 1 at point A (where the blue line passes through) youÂll see that the slope of that line is steep indicating that there is not much buffering going on. The solution to this problem is not to add more alkalinity (that slope is an inherent part of the bicarbonate system) but rather to reduce or eliminate your algae problem. More alkalinity wonÂt really solve this daily swing in pH...it might reduce it a little bit but the real solution is dealing with the algae.

Ammonia - short term spikes (after your fish eat, for example) are not going to have much impact on anything. You want your long-term levels to be at zero, of course. The first line of defense is your biofilter. In this case, bigger is better. I have yet to hear of anyone say they had too large a biofilter; the information provided by most commercial systems is - in my opinion - off by at least a factor of two if you have any fish in the pond. Your biofilter will rapidly convert the ammonia to nitrates without you really having to add anything. The resulting nitrates will be taken up by plants or can be reduced somewhat with water changes. Aeration will help remove ammonia - something you'll want to think about a bit come winter. The way aeration works is that when the pH is above about 7.8 or so you have ammonia in the form of ammonium hydroxide. In this form the ammonia gas can become stripped from solution as ammonia gas. Below a pH of 7 or so it becomes very difficult to remove ammonia from the water by bubbling. Since there is very little ammonia in the background concentration in the air the bubble released in the water attempts to come to some form of equilibrium bringing ammonia gas out of solution and into the air bubble. The bubble rises to the surface releasing the ammonia gas; the process repeats itself over and over. The smaller the bubbles the more surface area for gas exchange; the more air flowing the more bubbles and therefore the more surface area also. You donÂt have to use a bubbler....a stream or waterfalls will also do the same thing. There are chemicals you can add to lockup the ammonia but this should not be a real problem during once you have your biofilter working.

Well, IÂve blathered on long enough. And either totally overloaded you or created more questions than IÂve answered. But I hope this helps a bit so youÂll feel a bit more comfortable with your pond and what is going on.
ÂDavid

Hi,
The "N words" are flip sides of the same coin, and linked you have one to the other they are part of a cycle. If you want to get a feel for the process there are a number of good articles on the fishkeeping magazine sites. I like these sites because they do not get quite as technical as some of the others do. For the most part a stable established pond should have very minor issues for water parameters unless the water you are using is very high/low in PH or hardness. You will get swings until the pond stabilizes but I personally do not like to play with water parameters unless the fish are in distress. The cycle can take several weeks to get going. In my experience the only thing that causes the water to go way out of whack is too much fertilizer for the plants or too many fish for the biologic to handle. Wait for the prof.'s answer he will clear it all up for you.

Okay, let me see if I have studied hard enough. LOL.
"The more alkalinity you have the more resistance you will have to a pH crash"
#1. So does the mean I want the ph a little higher than 7, like about 8 or a little over? If so, I can add baking soda to raise it if needed? Or do I need to do a kh test instead of a ph test to determine this?
"low alkalinity and low-ish pH"
#2. How can you have both? Isn't a low-ish ph more acidic instead of alkaline?
"lets assume you have a pH of 8.3 and an alkalinity of 80 mg/L"
#3. If ph is 8.3, which is alkaline, where does the 80mg/L reading come from?
I only have the ph test so far. Can't find the others in town, so will have to order or go to pond store which is an hour away. But, anyway, my ph reading was 7.6
Thanks.

They say that the English language is one of the hardest to learn. It doesnt help that we use the same word with multiple meanings or words that look as if they are similar in concept. But then it would be boring otherwise, I guess. So here are a few fundamental definitions first (I wouldnt THINK of describing them as "basic" definitions, LOL!):
pH: a short-hand, numerical value for the concentration of the hydrogen ion. If you want more details let me know.
alkaline: describes the condition in which the pH is numerically higher than neutral (neutral = pH of 7 in water but only at 25°C)
acid conditions: pH is numerically less than neutral
alkalinity: the quantitative measure of the amount of a substance that will resist a downward change in pH (lowering).

The reason I bothered with the above is that pH and alkalinity are not the same thing. There are three forms of alkalinity that may be present in environmental systems. However, two of them are not significant for pHs below about 9.5 or 10.0 so I wont even bring them up. The third one, bicarbonate ion, is the dominate form of alkalinity in natural environments. You can have alkalinity at a pH of 8; you can have alkalinity at a pH of 6. In both cases the form of the alkalinity will be the bicarbonate ion even though in at pH=8 you have "alkaline" conditions and in the second case you have "acid" conditions. As to where you want your pH? Anything greater or equal to 7 is best for getting the most protection from a pH crash or sudden drop in pH (remember, alkalinity is the resistance to a decrease in pH). The reason I use 8.3 is that I dont have to "fight" the chemistry that will automatically set it at 8.3 when I add sodium bicarbonate. But if I really, really wanted to set the system up to minimize up and down swings of pH Id set the pH around 6.3 - which is not good for most fish or most of our plants. If you wanted it at some pH other than 8.3 youd add baking soda and then add an acid as necessary to adjust the pH to the desired value. Thats too much work for me; life is too short and plus the fact I might screw it up and overdose with the acid, whatever it might be. If your pH is above 7 (alkaline or basic conditions) the form of the alkalinity - the buffering species present to resist that potential drop in pH - is the bicarbonate ion, HCO3-; no other forms will be present in significant concentration until you get above 9.5 or 10.0 as mentioned above. The "80 mg/L" therefore refers to the concentration of the bicarbonate ion or alkalinity....not the pH. Dont worry about the units associated with the "mg/L" terminology since thats a whole other, confusing story! Hope this clarifies your questions.

Another issue (which I didnt really address but was mentioned by Squirelette) - nitrifying bacteria. The conventional wisdom used to be that dissolved ammonia would be oxidized by a group of bacteria known as Nitrosomonas. They would provide the first step and oxidize it to nitrite (NO2-1). Then a second group of bacteria would oxidize the nitrite (NO2-1) to nitrate (NO3-2) ....the nitrogen atom can have different valence states in the different ions. The nitrate ion is the most oxidized state for any form of nitrogen that you normally would see in your water. Both nitrite and nitrate are toxic for long term exposure of your fish so you ultimately want to reduce them to zero. Usually not a problem if you have plants in the water. However, currently the nitrifying scenario is viewed as being a bit more complex (heres a typical article if you REALLY want to bore yourself to sleep). But all we need to know is that we like nitrifiers in our system; we want nitrifiers in our ponds!!! I dont care whos doing the work as long as the work is getting done!! There is a minor problem: the nitrifiers are generally temperature sensitive; the dont do too much once the temperature drops below about 45°F or so. Just another reason to follow feeding recommendations come fall/winter.
But now Ill let you in on another little secret. If you want to create a bunch of controversy and many, many posts just mention the word "chloramines" in your heading (Im assuming that having buried it this far down in this post not many will jump on it!! LOL). Chloramines are used in many municipal water supplies to establish long-term disinfection residuals. Well, it turns out there is a little problem: nitrifying organisms will break the chloramines down!!! This is good news for those of us using the water to top off our ponds. So heres what I do: I run water to the pond through a timer/valve unit (battery operated) that only opens it for a set period. At this stage in life I might go to bed and forget to turn it off!!! LOL. The water passes through a carbon filter (whole-house unit) which despite claims to the contrary knocks out about 60% of chloramines. Then through a float valve in the skimmer as a somewhat-backup on how much water I add. And - heres the important part - it is diluted with incoming water all of which passes through my biofilter! Result? Chloramines? What chloramines? Theyre completely destroyed by the my nitrifying buddies in my biofilter!!!! I believe that I mentioned that having a honkin big biofilter is a good thing! LOL. Here are a couple of abstracts/articles on nitrifiers and chloramines if youre interested - just another aspect of your nitrogen, nitrite, nitrate question.Article 2 Article 3

Hope all this stuff is helping. Just keep asking questions if youre still confused or somehow you think I might be of help.
David

"Thank you," David.
I so appreciate the chemistry info.

It is helping and I thank you, too. Your second post clarified everything for me. One of these days, when I get the test kit, I will post the results and let you tell me more. You do a good job.

I taught him all he knows! LOL
"Horton"

Yep, all my misspelled words, poor phrasing...I get to blame Horton for it!!
---David

Ya'll are funny. Wise, but funny. LOL.