Pond Water pH and Quality Concerns

by Maggie

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)?

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.

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Aug 04, 2016
Pond Water
by: Grant

Hi Maggie

It sounds like you have found the source of the problem.

It's quite possible the ammonia converting bacteria aren't established yet, but as long as you are watching the ammonia level and doing water changes you wont go far wrong.

You haven't found definitive answers about winter feeding because winter temperatures are so variable.

As a general rule, I find with my fish that below 10C they aren't that interested in food. If the water temperature drops below 10C I stop feeding.

They will resume feeding above 10C at say 11-13C, but they don't eat much, probably half their normal amount or less.

Aug 01, 2016
by: Maggie

Firstly, thank-you for your response.

The pond seems to have 'fixed' itself. For the last four days the ammonia reading has been 0.0 ppm. It may have been caused by leaves from the surrounding plants, as I cleaned out a lot of plant matter (both living and dead) from the pond on the day I posted my questions.

I've been doing water changes on the quarantine tank and keeping a close eye on the fish, and the ammonia level is going down. The nitrite level is flat at 0 but the nitrate level is rising. Could it be possible that the bacteria for converting nitrite is established but the bacteria dealing with ammonia is struggling?

I'm careful with feeding the fish too. Since it's winter they are fed about once or twice a week. They get floating pellets and whatever they don't eat within about five minutes is removed using a net. I'm not sure if I'm feeding too often because I haven't been able to find any definitive answers online, I just know not to feed them every day when it's this cold.

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