Water problems dying fish

[Gerry]

My pond is approximately 800 gallons. There are 2 bio filters and lots of aeration. Until April I have 14 large goldfish that I have had for 10 years. Slowly they started dying. I noticed them at the surface getting air. After over half of them died I drained 3/4 of the pond and added tap water. The remaining fish (6) seemed to "perk up" but then they all died. My pond plants are fine and cover less than half of the pond. The water has turned green and I am now thinking I should drain it, clean the bottom and rocks and start over. I have had my pond for 15 years and have never had this problem but I am wondering what needs to be done without waisting money on more chemicals. So my questions are:

Could there be something in the bottom that is causing the fish to die or perhaps a toxins?
Should I just drain the entire pond, clean it and start over?
I read where barely bas might help or filtering the water using a carbon filter paper.

Any suggestions would be appreciated.

Thanks,
Gerry

 

[Meyer Jordan]

Have you tested your pond water? Taking into account that you only have Goldfish and this is an unexpected algae bloom, I tend to think that you have had an Ammonia spike.
Have you added any pond treatments recently or modified your biofiltration?

 

[Gerry]

My pond is approximately 800 gallons. There are 2 bio filters and lots of aeration. Until April I have 14 large goldfish that I have had for 10 years. Slowly they started dying. I noticed them at the surface getting air. After over half of them died I drained 3/4 of the pond and added tap water. The remaining fish (6) seemed to "perk up" but then they all died. My pond plants are fine and cover less than half of the pond. The water has turned green and I am now thinking I should drain it, clean the bottom and rocks and start over. I have had my pond for 15 years and have never had this problem but I am wondering what needs to be done without waisting money on more chemicals. So my questions are:

Could there be something in the bottom that is causing the fish to die or perhaps a toxins?
Should I just drain the entire pond, clean it and start over?
I read where barely bas might help or filtering the water using a carbon filter paper.

Any suggestions would be appreciated.

Thanks,
Gerry

I did add biogrowth as per my pond store. I had been using a water clarifier. I felt down to the bottom of the pond and there was quite a bit of black silty substance.

 

[Meyer Jordan]

there was quite a bit of black silty substance.

How thick would you estimate this sediment layer to be?
Explain "had been using a water clarifier" Was this a dechlor?
What is biogrowth? Unfamiliar with that product.

 

[Gerry]

How thick would you estimate this sediment layer to be?
Explain "had been using a water clarifier" Was this a dechlor?
What is biogrowth? Unfamiliar with that product.

It was a dechior and I am calling it biogrowth but I was told that I needed to add this product to build up the good working bacteria.

 

[Gerry]

It was a dechior and I am calling it biogrowth but I was told that I needed to add this product to build up the good working bacteria.

Silt on the bottom is between 1/4 and 1/2 inch.

 

[Meyer Jordan]

It was a dechior and I am calling it biogrowth but I was told that I needed to add this product to build up the good working bacteria.

Although not necessarily the cause of your problem, but a 10 year old pond does not need any bacteria added, The pond already supports the maximum possible population and if this was the powder form of bacteria it would contribute next to nothing to the nitrification process.
Do you have a test kit?

 

[Meyer Jordan]

Silt on the bottom is between 1/4 and 1/2 inch.

Not enough to be concerned about.

 

[Gerry]

Have you tested your pond water? Taking into account that you only have Goldfish and this is an unexpected algae bloom, I tend to think that you have had an Ammonia spike.
Have you added any pond treatments recently or modified your biofiltration?

I did test the water and barely recorded Amonina level. Ph Was high around 7.5-8.0 but I was told that goldfish like that.

 

[Gerry]

Would draining the pond, cleaning it be of any value or would I be destroying what is there?

 

[Lisak1]

Sorry to hear about your fish @Gerry - stick with @Meyer Jordan as he walks you through the process of determining what might have happened. He is very knowledgable and willing to help.

 

[Meyer Jordan]

I did test the water and barely recorded Amonina level. Ph Was high around 7.5-8.0 but I was told that goldfish like that.

When did you do this test? Was it before or after the fish died and what was the time difference between the test and the die-off?
7.5 - 8.0 is not a high pH for either Goldfish or Koi since their preference is 7.4 - 7.6.

Do not drain the pond without first determining the source of the problem. There are no fish left in the pond, correct?

 

[Gerry]

When did you do this test? Was it before or after the fish died and what was the time difference between the test and the die-off?
7.5 - 8.0 is not a high pH for either Goldfish or Koi since their preference is 7.4 - 7.6.

Do not drain the pond without first determining the source of the problem. There are no fish left in the pond, correct?

I tested the water after all of the fish died. I only tested for Amonia and PH. Amonia was negligible and Ph normal. After reading some responses on the forum I replaced the sponge filters with fibre fill to see if that helps to clear up the water. I removed most of the plants with the exception of 2 large ones.

 

[budgenator]

I did test the water and barely recorded Amonina level. Ph Was high around 7.5-8.0 but I was told that goldfish like that.

If you have fish dying and green water then the nitrite, nitrates and phosphate levels are important too. Taking plants out is probably counterproductive, and massive water changes can push you into New pond syndrome. Vacuum the bottom, but don't suck up more than 10 - 20% of the water each week. When you clean your filter elements the goal is to keep them unclogged not "clean", and don't rinse them with chlorinated water.

 

[Gerry]

Great suggestions. I will have to do 2 things, buy a test kit and a vacuum. Thanks!