I definitely would not add any fish until the water is corrected!! You should be able to obtain the correct chemicals from the fish shop or a pond shop!! A test kit is not that expensive for you to test the water yourself. Why put fish in when you know they will most likely suffer & die??? I have concrete blocks in my pond for plants to sit on, I don't think that is your problem.
Just my opinion!!
Dianne

Testing your pH is a start, but you need to test your kH, AKA total alkalinity or buffering. Of the two the kH is probably more important. The kH will affect the pH in ways that can be either good or bad depending on the situation. Adding chemicals to correct the pH might produce only a temporary effect because of the buffering from the kH and the concrete block itself.

My advice is check the kH, and proceed slowly. If you try to adjust the pH wait for it to stabilize before you add fish.

fish can survive quite nicely at a higher (or lower) pH, as long as it is stable. A pH that is constantly fluctuating because of your attempts to get it at a certain level is much more dangerous to fish. The people at fish shops LOVE to sell chemicals to adjust pH so ignore him. As long as it is stable, don't mess with it. What is the pH and hardness out of the tap?

Stable and high is better than fluctuating with chemicals (because you will forget it one week or go on vacation etc)

Let your pond mature a while I know the temptation to get fish in there is hard to resist. But don't succumb to the temptation to put some trash fish in there to test things.

Take daily for a few weeks and do a couple partial water changes during that time. If your PH is solid throughout, you just have a naturally high PH water and short of a water softener you are not going to be able to consistently keep it much lower.

Here in Arizona the PH coming out of the tap is at 8-8.1 and I have yet to lose a fish....which is not exactly a good thing. I figured like you that my new pond would probably kill a few or be too hard for koi or nice gold fish. So I bought some feeder gold fish who I figured I was saving a slow death in the petstore overcrowded gulag or a faster death as feeders. Well they lived and now I have some ugly brown,silver and orange goldfish. I love em cause im a pet guy but I wish I had the room for more of the pretty koi, comets and shibukins I have now. Also they will likely mate and make ugly babies :(

azponder,
I am going OT here but I bought 9 Sarrassas and 3 Shubunkins at the start of my pond 1.5 years ago. I thought I would have pretty babies. Today, I have about 40 -50 fish-some very pretty resembling their parents. Most are solid orange and short finned and about 15 are solid brown and short finned.
My point is even pretty fish can produce goldfish that do not look anything like the parents. Do not let it bother you.

lsst...you're right about pretty parents producing ugly babies. Consider the fact that a pair of grand champion koi may produce 100,000 fry in one spawn. Only 10% of those might survive after the first culling...the rest are destroyed. Then they are grown for a little while, and culled again....and only 10% of the original 10% are still kept to grow on further. My point is, that in the end, maybe 50 fish of those 100,000 will ever be sold, and of those, MAYBE one will be show quality. Koi and goldies have the genetics to produce WAY more ugly babies than pretty ones. And because in this world it's survival of the fittest (or the best camouflaged), the pretty babies often get eaten and the dull brown ones hide well enough to survive to adulthood.

And besides, some fish start out being ugly ducklings and some do change much later. I bought some comets at 5 inches long, don't know how old they were at that time. I was hoping for some sarasa's out of the bunch and when they arrived they were orange with 1 being white. I was disappointed, but they have turned out very pretty. The orange ones have gotten more red and the white one is about 8 to 10 inches now and is getting some orange scales scattered over his body. I went down to my daughters pond for the first time in a long time and there swimming around in her pond was about a 4-5 inch comet that was hatched last year in my pond and it is a georgeous reddish orange and white.Glenda

I got some of my prettiest comets when a Meijers here got one of those culls. The tank was teeming with hundreds of comets in all configurations at the low, low price of 10 cents each. The clerk thought I was probably nuts but cheerfully chased down the ones I wanted. I got Sarrasa, long finned comets etc. Of course not all of them survived, but the ones that did are some of my favorite fish. Be sure before you put any of those in the pond to treat them for parasites. Sandy

I had the same proproblem a high ph for me it took a test kit 61/2 cups of Vinegar to bring it down to 7.2