richyd said:
Still a newbie but I have experience with this. When I constructed the pond I used a lot of cement on the brickwork and waterfall which I did not use any sealer on. I had some fish and some koi at the time which were fine but the ph was gradually rising. Turned out to be lime in the cement leaking into the pond. It got as high as 9.0 at one point. I sealed the cement using G4. I know there are chemicals and the like out there to reduce the ph, I think tetra even do a product called "water balance"(think thats the name) which puts you PH and KH at the correct levels, but I wouldn't use this if you have fish.
My local aquatic guy recommended gradual 20% water changes weekly. It took time but my ph is now stable and buffered and all my fish are fine
pH "water balance" products compose of particular buffering solutions and minerals that raise your KH and also likely your calcium level.
Richyd, I bet ya your water's calcium concentration is quite low.
KH only stops your pH from falling. KH does not stop your pH from rising. Nature naturally lowers your pH and is often the predominant occurence in our ponds.
Calcium is what helps prevent your pH from reaching above 8.4. A high GH does not indicate a high calcium. GH is a test of many minerals plus calcium, but it is the presence of calcium that matters; this is how a GH test can be deceiving and not helpful.
As in nature, everything in pH chemistry is in balance. Free hydrogen ions (H+, this is predominately created by the nitrification process) and hydroxide (OH-, that is created by anaerobic conditions and algae) are always in equillibrium with water. So, when the H+ concentration goes up (pH goes down if KH is low). When the OH- concentration increase (pH goes up if calcium is low).
If calcium is not present to neutralize the carbonate (CO32-), then the carbonate reacts with water to increase the OH- concentration, which causes the pH to go up.
Lime is a general term for
calcium-containing
inorganic materials, in which
carbonates,
oxides and
hydroxides predominate. The predominance of hydroxides (OH-) in lime is what causes Lime to raise the pH.
Again, in our ponds, we most often have a predominance of H+ created due to nitrification and other decomposing so it takes the addition of a tremendous amount of algae or lime or other compounds for the pH of our pond to go up.
Richyd, I bet ya adding calcium chloride flakes would have fixed your high pH. Not for sure where in the UK you would get it, but here in the states we get it from the hardware store and it is the product with
zero additives.