It seems every time I test my PH, it's the darkest color, and my chart only goes to 9.0 so I don't really know how high it is. The fish seem to be doing ok, but I've never had it below 9.0 in the year I've been here. I have PH Down, but I always seem to forget after a couple days of treating. Do I need to be more vigilant on getting it down, or is it ok since the fish are doing ok? The nitrates test at the lowest level. The fish did breed over the spring. I have a 350 galloon pond with 5 large fish and about 11 small fish. There are no plants, though I'm trying to start a winter hardy lotus. I do have cat tails on the edge with roots that go in the water. It has a waterfall that falls over rocks and a pump "squirter" (for lack of the official term - I'm new to this). For cover I have a Japanese Maple by the edge and a cotton wood with branches that go over. During part of the day there is direct sun over most of the pond. That's why I'm trying to start the lotus. Haven't had much luck with it, though.

What is the pH of your tap water? Is it also that high? If so, then you might want to continue using pH down as needed or otherwise try to lower the pH because 9 is a big high. If your tap water is not that high in pH, there may be something in the pond such as cement or limestone that is leaching and increasing the pH. How are your hardness levels? They are usually really high with high pH.

Have you tested with just one pH test kit? If so, get another one and try it. I've tried a number of kits, and it seems they aren't very consistent. They often aren't that accurate either. Check the expiration date as well. Dip stick tests are the least accurate followed by liquid and then dry tab tests. There is also some interpretation of color matching required that often is hard to discern if the colors are close in hue.

If the fish seem to be doing ok, I wouldn't over-worry about the high pH but you should at least try to figure out the source and monitor the situation.

I have the liquid tester, where you add 5 drops. I tested the tap water, and it tests at between 7.5 and 7.0. I topped the water off, and it dropped down to 8.0 but I don't really trust it, as I treated it before I topped it off. I'll have to get to the pond store and get more PH Down though....

I suggest you get another pH test kit. It sounds also like the pH increase in occuring in the pond (not from the tap). In that case, water changes will help a lot to bring the pH down.

I tested my pond water yesterday five different ways:
Dip stick 1 - 6.8
Dip stick 2 - 8.4
Liquid - 7.2
Liquid (newer)- 7.8
pH meter at work (this is what it probably really is) - 6.82

My point is that different test kits give numbers all over the place and are hard to read, etc.

Well, that eased my worries a bit. I tested with my spa tester kit (I know, not an official pond tester, but...). I got a PH of 7.8, and a total alkalinity of 240 (which says for a spa is very high). Then I tried another spa test strip and got 400 ppm calcium hardness, PH of 7.5 and total alkalinity of 240 ppm. So I guess my PH is OK? What does the high total alkalinity represent? And is that bad for a pond, like it is for a spa?

Thanks for all the advice, by the way.

My pond used to have a low hardness and alkalinity since my well water is very soft. Most tap water is moderately hard. When I tested my pond a few days ago, I found the hardness (~GH) around 25-50 ppm and alkalinity (~KH) around 80-120 ppm using two dip stick tests (not very accurate of course). That's in the moderately soft to slightly hard area which is good. I read that 100 ppm total hardness is good for ponds with 80-150 ppm being ok. Your 400 ppm is very hard. Now, since your pH might be high, this makes sense as hardness and high pH usually go together. If your tap water is not high pH and hard, then possibly there is something leaching into the pond water like cement, limestone, leaching rocks, etc. The only real way to decrease hardness is to dilute the water with water that is softer (safe rain water, distilled water, any safe water that is lower in hardness). I'm not sure what the ideal alkalinity ranges are. I add baking soda to bring that up. Your alkalinity level may be ok. A pH under 8 is fine so your pH may be ok as well. Alkalinity represents the ability of the pond to maintain its pH or buffering capacity. It results mostly from HCO3- (bicarbonate) in the water. It can change as the carbon dioxide levels fluctuate in the pond as various animals, plants, and bacteria use and/or give off carbon dioxide. Alkalinity or temporary hardness is said to "feed" the biological filter bacteria and be good for the pond. Hardness is permanent hardness caused by calcium and magnesium mostly.

Most pond fish can easily handle a pH of 9.0, I know people with such a pH. As long as you acclimate new fish (as the pet store is probably not at a pH of 9, although it is possible), your fish should all be ok. You tested with other testers and reported a different pH. Try the 5 in 1 test strips... they are relatively new, and they test for the 5 major factors. I love these, and find them incredibly accurate.

What fish cannot handle is extreme pH swings. Changing your pH from 9 to 8 (if that is what you really did) is deadly to most fish. It is really dangerous trying to change something such as pH when you are trying to change the chemistry of the water altogether. So I would like to repeat what has been said - do not worry about your pH. You might not want to keep something like Neon Tetras in a pH of 9, but as for pond fish? I think they'd be fine. ;)

Do other rocks leach into the pond water besides concrete? I'm not totally sure what limestone is, but all the rocks seem fairly hard. Since I didn't put the pond in, I don't know what kind of rocks they are, but they don't seem particularly porous. There is no concrete directly around the pond. I do have 2 female dogs, and I've noticed lots of birds, a couple frogs and at least one snake (moved a rock to see what the rock under it looked like and saw it). With my dogs, I don't imagine I have too much other wild life around. The tap water goes through a water softner (Rainsoft) that uses potassium (instead of salt). I haven't changed out the water since I've lived here (a little over a year). How do I go about that, a little at a time? I have added as evaporation took it's tole, but not actually gone about trying to empty and refill... The fish apparently are fine with the water, as they bred over the spring. I have 5 adult and about 11-12 smaller (about an inch and a half to 2 inches long). I top off the pond about 2 or 3 times a week. Will plant life affect the hardness?

There are a few rocks that can leach. Those that raise the pH can be tested. If you put a piece of the rock in a small container and pour some acid on it. Vinegar will do. If it foams up, then it is a rock that can raise the pH.

To change the water, just pump out some of it (not all of it) or drain it by gravity with a hose. Then, refill. If you have city water and change more than 10%, you probably need to add dechlorinator with the water change. Most times ponds get water changes, it's small like 10-20% simply because of their size. Larger water changes can be detrimental because of the abrupt change in water chemistry and also because some microorganisms may be removed. The effect of plants on hardness is minimal compared to the water source and any sources of leaching.