Pond help - very very hard water!

Hi folks,

This is really a water chemistry question.

We have an ornamental pond with fountain in the garden. The pump for the fountain died, and to repair it we have had to completely drain the pond. In the next few day I will be refilling it, using water from our borehole. The water is incredibly hard, like over 400ppm of total alkalinity.

Because of location we have no way to collect and fill with rainwater, so it gets topped up periodically with more borewater. The problem has been that the total akalinity of the pond has increased a lot over time, to the point that our pond plants have been choked by limescale build-up on their leaves anywhere they touch the surface. I just jet washed two full buckets of limescale off the sides and bottom of the pond.

Given that we are refilling from scratch, with a clean pond and no plant life, what can I do to reduce the total alkalinity?

In our swimming pool we add HCl to reduce the pH, allow it to equilibrate over a day or so, then repeat the process until the TA and pH are in the right place. Is this process safe for a pond with plants and fish? My instinct is yes. The acid will break down the carbonate ions, leaving Ca+ and Cl- ions. Is there any reason why this won't work out? I feel it has to be better than not attempting to lower the TA, given the problems we observed over the past 8 years or so.

can we go back with what you wrote.
Why cant you catch rainwater and store it in a tank for topping up the pond? My signature has a link to how.

I'm not a chemist or water specialist... though I have dealt with some fairly hard water before.

My first thought is to ask how big is this ornamental pond? Something less than 50gallons and I would be tempted to just buy bottled water for it. For larger, could you get one of those trucks they use for filling swimming pools to come by and pump some water in?

Around 6 cubic meters. And a tanker won't help - it would be coming from the same ground water supply!

John C Daley wrote:can we go back with what you wrote.
Why cant you catch rainwater and store it in a tank for topping up the pond? My signature has a link to how.

Not viable here. It is an ancient listed building. We can't change the external look of it at all - no storage tanks, visible plumbing etc... And that doesn't help with our immediate issue of needing to refill it from scratch in the next few days to get the plants put back in.

I'd really appreciate someone addressing the actual question about water chemistry in a pond. I do understand what the "ideal" alternatives would be, and how to implement them. They aren't possible. I don't want to have to write an essay explaining why each alternative won't work.

Would a circulating pump, solar driven, work by putting the water through a suitable 'filter' filled with the substance that 'fixes' the water?

This company has an idea for domestic water which may generate ideas.
https://www.uswatersystems.com/blog/what-is-hard-water

managing-high-ph-& hardness in-freshwater-ponds