It's been about 40 years since college chemestry, so let me just tell you this: I'm a plumbing contractor and for people who pee in their toilets and don't flush right away ("If it's yellow, let it mellow" mentality), the chlorine in the water reacts with the soluble carbonates in urine and they precipitate out (form solids inside the toilet). This eventually causes the toilet to flush incorrectly.

I said all that to say this: Adding vinegar (acetic acid) will soften the concretions over time. So, to answer your question, if asked in reverse: Yes!

Adding any kind or any amount of acid to your hydroponic set-up will drastically affect the pH!

Hope that helps some.

Some commercial growers will use nitric acid to neutralize calcium carbonate and magnesium carbonate in their water. I believe the products from the reactions are magnesium nitrate, calcium nitrate and carbon dioxide. Concentrated nitric acid is too dangerous for a person to keep around their house or garage though.

Vinegar is a dilute acetic acid. Acetic acid is what hurts the plants. Concentrated forms of it are sold as more environmentally friendly contact herbicide which you can read about here:

http://www.pesticide.org/pubs/alts/weeds/vinegarinherbicides.html

This source says the acidic qualities destroy the cell walls if the acetic acid is sufficiently concentrated. Spraying the vinegar we keep in our kitchens may not do the job for much more than small juvenile weeds.

If this were indeed true then calcium carbonate should diminish the effect. The acetic acid would form partially into calcium acetate and neutralize it's acetic pH. Calcium acetate's pH is about 7.5, according to this MSDS.

http://www.jtbaker.com/msds/englishhtml/c0266.htm

According to wikipedia calcium acetate is used as an additive in candy. Who knew? You could try mixing acetic acid with classroom chalk or tums, then applying it to a plant and/or soil and see what happens. If you use baking soda you will be introducing some sodium which isn't going to be desirable.

With a bit more searching I found this subject has already been discussed .. and right here on this very forum! Starting with third post.
"I get soluble calcium by dissolving sea shells in vinegar. Let ±50g of shells soak in 1 liter of white vinegar. After about 24 hours you can boil the lot in a stainless steel pot for about an hour. Then filter the liquid (I use a coffee filter [LOL]) to remove the excess of shells and make-up the volume to 1 litre.
This way you obtain a calcium acetate solution that contains 15 grams of calcium per litre."

"? Are you able to estimate the grams of Ca that egg shells, substituted for sea shells, would yield in your formulation ?
(The egg shell in vinegar extract, for soluble calcium, was told me by an old country doctor over a quarter of a century ago for use as a human nutritional supplement of calcium.)"

"It would be the same.
The amount of calcium(Ca) that will dissolve as acetate in 1L of white vinegar (5%) - irrespective of its source - is ±15g (in theory: 16.7g).
Just dissolve egg shells untill they no longer dissolve."

"when making the calcium acetate, is boiling required? and what does that part do? I was thinking of just dumping egg shells and vinegar into a glass bottle then skimming liquid off the top as needed as a calcium supplement. since the concentraition will always be 15ppm, the idea is just get as much as required for the concentration I want to make up."

"I suppose that could work. The boiling is intended to remove any residual acid. Maybe you should test the pH to make sure(?)"

I knew this looked familiar. Ask Greystoke about this. He's the Garden Web chemistry guru in my opinion.

Good call. He's exactly who started the above!

Here is a link that might be useful: Cited Post

What is there to say? Most has been said, except . . . I do not believe that vinegar itself (as opposed to other mild acids, such as citric acid) is a herbicide. I think its just the acidity that does the trick (in my opinion). So . . if you neutralize it with calcium, the effect should be gone.
Besides . . . I've used this for years without any bad results. It's handy to have around when you need to add calcium.

Hello there! I hope I´m not too late.
Plants can only absorb soluble calcium, and the eggshells are Calcium Carbonate that is very insoluble. So it´s better to buy some cheap Calcium Carbonate than using eggshells. But you have to disolve Calcium Carbonate. Wait!! there´s a little secret.
Easy! Just add to Calcium Carbonate some water and Citric Acid. Citric Acid complex calcium and eliminates carbonate (CO2), and it´s a very acid with buffer capacity. ;-)
How much you may ask? That´s your work!