The blocks I think we're gonna go with

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Yesterday we went looking for ideas on what to use to build our next pond, and we saw these 8"x17" blocks we really liked! The liner will separate the blocks from the water, but I was wondering if it'd be ok to also used them inside the pond, in the step down from the plant section to the main pond, or would it raise the (already high) ph too much?
20171007_112950.jpg
 
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Not sure about ph but use underlayment between them and the liner if used in the pond.
 
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I would strongly advise against using any stone or rock that has sharp edges below the water line. Come spawning season and you may end up with a few minced fish!
I can't believe I did't think of that,I should have known better since we had to remove and grind most of the stones, after the contractor was done, because they had sharp edges!
Thank you so much @Meyer Jordan for bringing this up!
 
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Oh, how exciting.....another pond build ! Will it be a separate pond, or are you making changes to your current one?
 

Meyer Jordan

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I can't believe I did't think of that,I should have known better since we had to remove and grind most of the stones, after the contractor was done, because they had sharp edges!
Thank you so much @Meyer Jordan for bringing this up!

Might have been a contractor by legal classification, but they obviously knew very little about constructing functioning ponds.
 
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Oh, how exciting.....another pond build ! Will it be a separate pond, or are you making changes to your current one?
It's a new pond!
There isn't much that I can do to the existing pond, other than swap stones if I find better ones!
My next pond will be a couple of feet above ground,with a flat top, and it will have a shelf that way I can sit on the edge and interact with my fish...something I cannot do in the existing pond and is the main reason why I'm building another one.
Might have been a contractor by legal classification, but they obviously knew very little about constructing functioning ponds.
You got that right!
 
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I wouldn't use them inside your pond or where they can touch the water. Anything made of Portland cement is fine for ponds, but blocks like these will make your water very alkaline.
 

Meyer Jordan

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I wouldn't use them inside your pond or where they can touch the water. Anything made of Portland cement is fine for ponds, but blocks like these will make your water very alkaline.

I have always been led to believe that any concrete block is made primarily of portland cement, aggregate, sand and water. What ingredient in these blocks would make them more alkaline?
 
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I'm not sure if I can even find out what's in these blocks, they are called "Landscaping concrete blocks", they have a very faint shade of blue, and tan, but other than that it looks like concrete.
My ph is already high though so I can't take any chances, I will only use them out of the water
 

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This might be an appropriate time to address another of those 'myths', 'Old wives tales' associated with ponds. That anything containing limestone will adversely affect the pH of a pond's water column.
Limestone is primarily Calcium carbonate. Sound familiar? It should as it is the mineral that KH is derived from. Adding limestone, in any form, to a pond will increase the KH which, as we all know, serves to stabilize the pH. In and of itself,KH will not raise or lower the pH of a pond's water column.
One ounce of lime will raise the Alkalinity approximately one (1) point for every 4500 gallons.It is used qu9ite often to stabilize the pH in fishery and farm ponds.
Any leachate occurring from concrete, either poured or block form will be well below this above given rate so it would be slow to even affect the Alkalinity (KH).
Additionally, lime (Calcium carbonate) will add a certain level of CO2 to the water which aids in photosynthesis.
One could infer that concrete blocks could be a beneficial addition to the overall water chemistry
 
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When I joined this Forum last year, I read about high ph and concrete and immediately removed every concrete pot my husband had made for the plants in the pond, but my ph never changed one bit, so after a while, I put them all back in the water
 
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Meyer this is from wikipedia re: concrete blocks
Composition[edit]
Concrete blocks are made from cast concrete (e.g. Portland cement and aggregate, usually sand and fine gravel, for high-density blocks). Lower density blocks may use industrial wastes, such as fly ash or bottom ash, as an aggregate.[2] Lightweight blocks can also be produced using autoclaved aerated concrete.

When I buy cement for our building projects there are lots of choices besides Portland cement at the local supply store.
 

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