Pond Water pH and Quality Concerns

by Maggie
(Australia)

I moved back home with my mother relatively recently and started taking over maintenance of the fish pond.

Anyway, for the last month and a half, the pH has been quite low. The first pH test kit was reading about 6.6 so I bought some pH adjustment liquid to try to raise it. I wanted to do it in increments of about 0.2 every two or three days but the next day it would be back at 6.6.

Today, using an API test kit, it read 6.4. The goldfish seem perfectly fine but I'm worried that the pH is falling and I can't seem to stop it.

What should I do? It's winter here in Australia and it's been raining a lot, could that be a contributing factor?

Also, despite being an established pond, when I checked the ammonia, nitrite and nitrate I found something that I've never seen in my aquariums.

The readings were as follows:
Ammonia - 0.25 ppm
Nitrite - 0.00 ppm
Nitrate - 0.00 ppm
We have live plants in our pond which I can only assume is why the nitrate is so low, but is it normal for there to always be ammonia present?

Finally, I asked a question about inbreeding last week and have since set up a quarantine tank. I used some water from the pond and a portion of pond filter foam to kick start the nitrogen cycle on the quarantine tank and tested the parameters before adding two new fish. Today, 24 hours after adding the fish, the test results were as follows:
pH - 8.0
Ammonia - 1.0 ppm
Nitrite - 0.0 ppm
Nitrate - 5.0 ppm

I have a few questions. Is this pH too high? Is it normal for the Ammonia to spike after adding fish (again, I never had that happen in my tropical aquariums, or at least never noticed it)?

What is the 'maximum' tolerable Ammonia and Nitrite level (I've seen people suggest a variety of different maximums from 0-1 ppm)?

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Grant's Reply


Hi Maggie

Rain water doesn't lower pH unless you have acid rain, which is a real problem in polluted cities.

I'm not aware of any city in Australia with that sort of problem, especially ones that have a lot of rain.

The ammonia reading is strange with the nitrate reading being zero. Ammonia being at the start of the "cycle" and nitrate at the end, I would have expected zero ammonia and say 5-10 ppm of nitrates.

I'm very suspicious of your pond water. Ammonia should be close to zero, especially in winter.

Are you sure nothing large has died in the pond?

Notice how you had a spike of ammonia in your quarantine tank when you used pond water plus some filter material to cycle the tank.

Any decaying material is going to end up in the filter, so you may have transferred the problem to the quarantine tank.

As an aside, any diseases you pond fish have, will now be transferred to your new fish. Have a read of the E-Zine back issue #024 on quarantining new arrivals.

Ammonia levels should be at zero. 1 ppm is too high. 4 ppm kills fish.
Nitrates can be quite high, up to 300 ppm, but Goldfish have to be in very poor conditions for it to get that high. Aim for around 20-30 ppm max.

Perfect pH is 7.4, so 8.0 isn't a problem. It's strange that it is that high considering the pond water was 6.4.

My suggestion would be a 50% water change immediately, and keep changing 50% of the water daily until the ammonia level is zero. Remove the pond filter media as well, there is enough ammonia present.

Water can spike after fish have been added, but 24 hours is a bit quick. I think it is the pond filter media in a smaller volume of water.

One last question, are you feeding to the temperature? Are the fish leaving food uneaten?

Don't feed them for a few days and retest the water.