PH 9+ in my pond

[juanprieto]

I have had two large Koi which I have had for 3 years suddenly die off. They have no outward signs of disease. I did find them with a rather large slime coat. Not sure if this is because they were dead for several hours before I found them.

The pond is about 2000 gallons and I have never had any major issues with my Koi. I tested the water and will show the findings below.

I noticed that the PH of the pond is around 9 based on a wide range pH test. I am in Miami and we have pH high water all the time. It had been around 8 since I started the pond. The only thing that has changed in the pond is that my UV light went out for some time and I just replaced it. I had a large algae growth as a result. The water was green. String algae was not present. It's been a week since I put in the new UV light and the green water is gone.

I thought to do several water changes over the next few days to get the pH back down a bit but when I tested the city water it too showed a pH of 9+. Now I don't know how to handle the problem. A water change won't reduce the pH due to the city water being high also. I thought about adding baking soda as a buffer but as you see in the chemistry results carbonate is at 120 which is good. I don't want to lose any more fish. Any insight would be very appreciated! See chemistry results for pond and city water below.

Pond Water results:

Ph 7.2
Wide Range PH >9.0
Ph Tap water 7.0
Ammonia 0
Nitrite 0
Nitrate 0
Phosphate (PO4) 3.5ppm
Iron 0ppm
Copper 3ppm
General Hardness (CACO3) 0
Free chlorine 0
Alkalinity (total) 120ppm
Carbonate (KH) 120ppm

—————————————————————
Tap water( city) result:

Iron 0
Copper 0.5ppm
Nitrarte 0
Nitrite 0
General hardness 10
Chlorine .25
Total alkalinity 80ppm
Carbonate(KH) 80ppm
Ph 7.4 with litmus paper
Wide range Ph >9

 

[JRS]

Sorry to hear about your fish.

Other than the high pH, which I do not think would kill an acclimated fish, I am wondering if perhaps the influx of dead algae caused the dissolved oxygen or water quality to decrease temporarily. Oxygen is often an issue when just the bigger fish die; although not as likely when water temps. are cooler.

What other fish do you have in the pond?

 

[WaterGardener]

You need a high range pH kit. The wide range one is not very accurate at the high or low end. It's usually used just to let you know that you need a different kit! So the reading may not be as high as you might think.

A high pH is not normally a problem and fish can adapt to it.

 

[juanprieto]

Sorry to hear about your fish.

Other than the high pH, which I do not think would kill an acclimated fish, I am wondering if perhaps the influx of dead algae caused the dissolved oxygen or water quality to decrease temporarily. Oxygen is often an issue when just the bigger fish die; although not as likely when water temps. are cooler.

What other fish do you have in the pond?

I think that might be it as well. I have no way of knowing. Perhaps the sudden algae death triggered something. I don't know. I do have two waterfalls going 24/7 and an aerator so pretty sure low oxygen is not a concern. Plus the fish were not struggling to breathe prior to them dying.

 

[juanprieto]

Sorry to hear about your fish.

Other than the high pH, which I do not think would kill an acclimated fish, I am wondering if perhaps the influx of dead algae caused the dissolved oxygen or water quality to decrease temporarily. Oxygen is often an issue when just the bigger fish die; although not as likely when water temps. are cooler.

What other fish do you have in the pond?

I have 7 Koi now and about 3 fat goldfish.

 

[juanprieto]

You need a high range pH kit. The wide range one is not very accurate at the high or low end. It's usually used just to let you know that you need a different kit! So the reading may not be as high as you might think.

A high pH is not normally a problem and fish can adapt to it.

Ok I will look for one on Amazon. Thanks!

 

[Pablo]

I have 7 Koi now and about 3 fat goldfish.

for a 2000 gallon pond having 9 koi may have been too much. Some here will probably comment but you might have about double what you should have in that size pond. But maybe you have a great filtration setup and can get away with it.

 

[juanprieto]

for a 2000 gallon pond having 9 koi may have been too much. Some here will probably comment but you might have about double what you should have in that size pond. But maybe you have a great filtration setup and can get away with it.

I have had them for almost 3 years without issue. I have a large Oase filtration system and two large aquascape biofalls.

 

[Mgessert]

I’m guessing they’ve grown in three years, resulting in increased fish mass in the same size system.

 

[Pablo]

I have had them for almost 3 years without issue. I have a large Oase filtration system and two large aquascape biofalls.

I know you mentioned in another thread that you had some down time because of issues with Aquascape. Could be that you have little margin for error with that many fish. That is why @GBBUDD mentioned having backup plans. I dont even have any koi yet so I am no expert at all, just seeing what other people have mentioned here about fish load etc it seems like it is tough to keep a high number of koi because of how large they get.

 

[GBBUDD]

Ph 7.2
Wide Range PH >9.0

I don't believe this is possible, ph is one number. If i am not mistaken your looking at two test kits one can not reach above neutral and the high is a second means of testing sob your low number is just the max that that test will go and you need to use the high ph to find the higher number that your pond and mine are at. I add baking soda to keep my kh up there so my ph is a high of 8.4

 

[WaterGardener]

My pond's pH was 9.0 on the high range test when my pond was new. I'm convinced it was from the mortar in the rocks leaching into the water. It stayed there for a few months, then gradually fell to where it has been for the last 8+ years, 8.3.

The fish were fine, even though they were moved from the lower pH and abruptly dumped into the new pond. Maybe not the best way to do it, but I didn't know any better at the time.

Not sure I understand what you are saying @GBBUDD. Why it that not possible?

 

[GBBUDD]

My pond's pH was 9.0 on the high range test when my pond was new. I'm convinced it was from the mortar in the rocks leaching into the water. It stayed there for a few months, then gradually fell to where it has been for the last 8+ years, 8.3.

The fish were fine, even though they were moved from the lower pH and abruptly dumped into the new pond. Maybe not the best way to do it, but I didn't know any better at the time.

Not sure I understand what you are saying @GBBUDD. Why it that not possible?

i was reading it as he has a ph of 7.2 and the wide range / high ph of 90 unless its morning and afternoon ph and its thats the case thats a big fluctuation i'd think the kh would be low

 

[WaterGardener]

Thanks. I didn't even see the 7.2 pH with the pond water. That is strange and something is definitely off there.

Don't know what type tests he is using. Strips maybe for everything except for the wide range test? I had thought that might be the case from the list of parameters and almost asked about that.

Looks like we need more info.