It depends. What sort of fish do you have in your pond? Any amphibians? Snails?
Also, why are you adding salt? It's useful as a medication, but the main reason people add salt is that it will cause fish to secrete a thicker slime coat. And the reason they will secrete more slime is that they are freshwater fish, and need to protect themselves from the salt. Many disagree with me, of course, but it seems to me that most of the fish we keep evolved for millions of years in water without much salt, and hence, they're really better off without it.
Some people swear by it and some people maintain that it is bad for freshwater fish.
I'm certainly not going to dose it to anywhere near the concentration of sea water and I'm not entirely convinced that salt is bad for freshwater fish. You need to forget the word salt and think in terms of osmotic potential.
Anyway, I've dosed the more common 0.1% and the fish really seam to be perky.
Orfe are said to be more sensitive to salt than koi or goldfish, but I'm not sure what their limits are.
I'm certainly not going to dose it to anywhere near the concentration of sea water and I'm not entirely convinced that salt is bad for freshwater fish.
I understand that you're not going to try to turn your pond into the ocean, but why raise salt above the level for which the fish evolved? I know many people add low levels of salt as a matter of course, and it doesn't seem to be doing too much harm. But does it really do that much good in the long run?
I think the reason for the conflicting opinions on this one is that the effects are subtle and the subject has never been adequately studied. Whatever theory you believe, it's easy to interpret what you see as confirmation. I claim no certain knowledge. But if it isn't broken, I'd rather not try to fix it.
You need to forget the word salt and think in terms of osmotic potential.
I've forgotten enough already. But whether it's salinity or osmotic potential, I think the ideal is still as close as you can get to the environment the fish would have in the wild. There should be no osmotic stress for a healthy fish in the sort of water for which it was born.
Now, I agree that if a heron puts a big hole in one of your fish, some salt might help the fish maintain equilibrium until it heals. But one trouble with using medications all the time is that the fish and their pathogens will adapt to the drug, and then the it won't be as effective. I honestly don't know how big a factor is that with salt, but some of the "experts" believe that it's better to wait until you actually need salt, and that makes sense to me.
BigKev wrote: You need to forget the word salt and think in terms of osmotic potential.
We've had a big discussion with some very knowledgeable experts on this site in the past about this very subject and it was osmotic potential that concerns me most. By adding salt you are changing the osmotic pressures to that which the fish is ill equipped to deal with. Short term salt certainly has its uses and many old hands in pond keeping swear by it, but I feel salt is vastly overused as a cure-all and not required to have healthy fish. So the short answer to your question is that the correct concentration (in my opinion) is 0%
We've had this debate a number of times already, to the point it was included in the March newsletter and LHG made a specific thread about it.
Freshwater fish have no need to have salt added to their water at all, except for the treatment of a number of conditions. Keeping salt in the tank on a permanent basis suppresses the fish's immune system, allows for pathogenic resistance, and impacts the fish's renal and vascular systems.
I have read that it is good for pond fish. Simple as that.
I have my algae under control by building a pergola over the pond and covering with read matting. The filtration is adequate to a factor of 4 times the pond volume.
Simply trying to do the best I can for their environment.
I have added a low dose of salt and I must say the fish really seem to have perked up. Their colours look great and the comet I was worried about looks fine.
My Orfe, however, have stopped feeding. I changed the food at the same time (because I had run out. No other reason) so it could be that. I am going to get some of the old food today and hopefully they will feed again.
If not, I will have learned a lesson and the pondovac will be put to good use again.
I'll report back later as I think this is an important issue and any empirical data will be useful for others.