Question
You said sulfuric acid, I know in a swimming pool you can use muratic acid to lower ph, will that harm the koi in small doses?
I don't like you!!! You know how much time I had building the falls? just kidding. I was afraid of that, but I hoped I had enough volume of water it wouldn't effect me that much. thanks very much, its nice to find someone that knows what their talking about
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Followup To

Question -
Robyn.
I have a 35x60 pond I built in march this year all is fine except green water. The PH is way over 9 thats as hi as the test kit went. I trie the barley extract, with no help. The fish are happy, lots of babies this year, both koi and goldfish. Plants on the other hand not so good. We have 40 lillies which I fertilized with tablets in the spring, and a lot of hyacins, and water lettice which we got from my parents. They have 6 ponds and have been ponding over 20 years. The largest pond is 20x15x3 deep. Their lillies, hyacins, and lettice are unreal. Mine did fine till the green came, The lillies are yellowed around the edges, hyacins all but died as well as the lettice.
 Where can I get a good test kit for ponds? What will salt do? What all should I test for?
 I have a biotech screenex 18 filter with 5k gph pump, modified 300 lb sand filter with plastic bio-bead media at 10k gph, and a 5ft dia x30"  deep homemaid gravel filled bio filter with 10k gph pump feeding a 3ft tall x 5ft wide waterfalls maid from layers of flat LIMESTONE, is this my problem?

Nitrites, Nitrates, Alkilanity, PH, or salt ? Why the green, and dead or barely alive plants?

Thanks, Scott

Answer -
Wow, that's a nice big pond!  With a high pH like that, it is not a surprise that the plants would be doing poorly.  They don't like it.  Also, plants don't do as well in a new pond that's not established.  You already know your problem.  It's the limestone.  It's leaching into the pond raising the pH and probably the hardness.  You should test the hardness.  The problem will remain until you can get the limestone out.  You can add acid but it would have a temporary effect.  pH fluctuations can harm the fish more than a constantly high pH.  Have you tested the pH of your water from the tap for comparison?  Some tap water is high in pH.

I buy most of my supplies from That Pet Place and Drs. Foster and Smith.  Here is one test kit with a few tests in it.  I normally buy my test kits individually.  I have them for pH, hardness, alkalinity, ammonia, nitrite, nitrate, salt, and oxygen.  It would be good to have all those but you need at least pH, hardness, ammonia, and nitrite.
http://www.thatpetplace.com/Products/KW/pond%2ctest%2ckit/Class//T1/W55AX+1044+0

Here's a description of salt use in aquariums that I wrote.  Basically in ponds, it deters bacteria, fungus, and parasites and helps the fish with osmotic regulation.
http://www.fishpondinfo.com/health3.htm#salt
I never add more than half the recommended dose for salt for planted ponds (on the bottle); plants hate it.

Your pump, filter, and waterfall systems sounds extensive but you have a big pond.  It's hard for me to say if it's enough without seeing it in action but it sounds pretty good.

My page on algae control:  http://www.fishpondinfo.com/plants/algae2.htm

From a page in my algae section:
"Check the pond's pH. If it is overly high (above 8), then finding a way to lower it may help reduce algae. In the long term, it is better to deal with the water chemistry that you are given then to try to adjust it all the time but short term, adding a pH-Down solution (H2SO4 or sulfuric acid) may help if the pond's pH is high."

Algae likes high pH.  Plants do not.  Algae can cause the pH to go even higher.  Get rid of the limestone.  Sorry!


Good luck!

Robyn  

Answer
The pond chemical sold as pH down is sulfuric acid, or at the least the one I bought.  Muriatic acid is another name for hydrochloric acid which is not as strong as sulfuric acid.  In low enough amounts, either acid is safe.  Now, if you poured a concentrate in one spot, and a fish swam by, that would kill him.  You have to dilute it a lot in a lot of water and disperse it around the pond.  It's really hard to know how much you'll need especially with the limestone buffering the water at a pH probably near 9 or more.

I will add you to my huge list of people who don't like me.  I don't know what I'm talking about.