Question
Thanks Robyn!
I do have a mechanical filter that pumps through to a bio filter and out a waterfall. I did not notice any gasping, but because I did not know what else to do while researching, I did add two aquarium bubblers that I happened to have sitting here. Has not seemed to make a differencein the 3 days they've been there. One of the two fish that died later that day seemed to be swimming erratically and almost trying to "beach" himself or prop himself up before he died.
I try very hard to be careful what I use in the yard anywhere near the pond, but I suppose runoff of lawn fertilizer/weed control is a possibility with all the rain we've had. Is there a remedy?
I have been watching the pH, but was not aware of the need for these other tests until researching this problem. Will look into this and the "good bacteria" right away.
The lettuce and hyacinths that I added when I added the new fish are looking very bad, though my marginals and lilies are beautiful. Does this provide any clues? You say "add plants"...Do you have suggestions for what plants I should add?
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Followup To
Question -
Our pond is exactly one-year old. Fairly small 8x13x2.5. We started with 8 fish (all various forms of goldfish), ended last season with 7. Wintered them in the house. Lost one more. Beautiful pond last year. Clouded up briefly when we added new plants. Cleared on it's own. Minimal stringy algae problems, that cleared with one treatment and the addition of some fresh barley straw to our filter.
This year, after cleaning out old leaves and silt, we put our 6 fish back in our pond. We bought two new marginal plants, a couple of floaters,and 4 more fish for a total of 10. Within three days the water clouded. It did not clear. Now it is a murkey green. I cannot see the bottom of the pond. Four days ago all 10 of the fish were at their usual, they rushed to the surface as we approached the pond , to be fed. And swam off when they'd had their fill. Two days ago I walked out to find 2 dead, 2 more died that day, and 6 were nowhere to be seen. today i have had brief glimpses of one and he does not appear well. The pH is 7.5. The water is green. Algae treatment made no change. We live in Ohio and have had several inches of rain in the past two weeks. The water level is higher than normal. Help! What is wrong and how do I save the remaining fish?
Answer -
There are many possibilities for what is wrong.  What kind of water movement, aeration, and filtration do you have?  If there's not a lot of aeration, have you checked the oxygen levels?  Gasping usually precedes oxygen problems.  With ponds with a lot of algae, the oxygen levels will rise during the day and crash at night.  pH will also change day and night.  Check pH at dawn, noon, and dusk.  How much does it change?  A pH of 7.5 is very good but what time of the day was it?  Algaecides may do more harm than good.  Read over my algae page at http://www.fishpondinfo.com/algae2.htm for some ideas.

Did you quarantine the new fish?  If not, they could have brought in who knows what that caused the deaths.  It's rained a lot lately you say.  Did dirt run into the pond?  Is fertilizer or chemicals used on the land around the pond that could wash in?  Rain will dilute the pond and change the pond chemistry, sometimes making it dangerous.  These are all possibilities.

Here are some suggestions:  Increase aeration and filtration with a larger filter or another smaller one and a large air stone or fountain to aerate the water; add more good bacteria (I use BZT from united-tech.com); add more plants; don't add any more animals for now; test pH three times during the day for a few days to see what it's doing; test ammonia, nitrite, and oxygen to see if they're okay; examine any dead fish for any symptoms (spots, lumps, injuries, etc.); and see my site for more ideas.  When there are algae blooms and/or when chemicals are added to kill the algae, heavy aeration is required to keep the fish safe from the resulting crashes in oxygen.

Good luck!

Robyn
fishpondinfo.com

Answer
When fish try desperately to get out of the water, poisoning is often a cause.  This can be due to ammonia, nitrite, pesticide/herbicide/chemical runoff, or direct poisoning (humans can be nasty).  The remedy is a larger water change ASAP with the addition of dechlorinator if you have city water.  Check the pH, ammonia, and nitrite levels. The addition of a bag of activated carbon into the filter will also help remove any toxins that may be in there.  Run it for a week and then get rid of it (poisons can leach back out).  Add the carbon after the water change.  It's not uncommon for floating plants to do poorly in ponds for the first few years, mine did.  You can add potash (potassium) to help.  It can be bought as that or in Flora Fin by Tetra I think it is.  This helps floaters that yellow.  There are so many plants!  See my section on veggie filters at http://www.fishpondinfo.com/plant3.htm for species that are good at filtering out things in ponds.