Question
QUESTION:   Hi, this is my first full year with my new pond. It's roughly 2800 gals with a waterfall and almost entirely 3 ft deep. Living in NC and having well water, my water is super soft (about 20 GH). All other readings are at good levels, even PH. I'm using test strips that test for 5 levels. What's the safest (and quickest way) to correct hardness w/o throwing the PH out of whack?
ANSWER: I just answered the same question yesterday!  I have super soft well water myself.  For my pond, I add some baking soda each week.  Baking soda, which is sodium bicarbonate, raises the alkalinity.  It will buffer the water without raising the pH too much.  It doesn't raise regular hardness. For that, you can add calcium carbonate or just put in some bags of crushed oyster shells (from a farm feed store, sold for chickens) or crushed coral (sold by aquarium stores for marine tanks).  They will slowly dissolve and raise the hardness but also the pH.  pH and hardness usually go hand in hand.  As someone with soft water, I can say the pond does fine.  I add maybe a quarter cup of baking soda at most to my 1800 gallon pond once a week and keep two mesh bags with the oyster shell and coral in the filter.  Yet, my pond water is always soft and pH near 7.5 or so.  The alkalinity though at least registers on the test kit!  It doesn't from the tap.  My well water is almost distilled.  Good luck!

Robyn
fishpondinfo.com

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QUESTION: Thanks! I've already added baking soda for the PH and now will add calcium carbonate. Are all sea shells OK or just oyster shells?

Answer
Oyster shells are easy to get.  I get a 50 pound bag of crushed oyster shells for a few dollars at the feed store for my chickens.  Since it's crushed, it dissolves slowly over time more readily than whole shells.  You can use other shells from snails, conch, clams, etc. as well as oyster shell and dead coral (crushed coral).  Basically, if it's dead and aged and mostly just the calcium left, you can use that.