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The Goldfish Gazette, Issue #116 PH impact on fry growth
August 29, 2023

Goldfish Care Tips

A Free Monthly Resource For Goldfish Enthusiasts
August 2023
Issue #116

In This Issue
PH impact on fry growth

Goldfish prefer hard water with a Carbonate Hardness above 5 and a General Hardness above 6, but will tolerate a wide range of water parameters as adults, but is this the case with fry?

PH Impact on Fry Growth

Following on from last month’s e-Zine concerning KH and GH levels and how it affected the growth of Goldfish fry, what came to light was how the pH level also has a marked affect on the development of young Goldfish.

There have been many growth studies done on carp because they are the most commonly raised fish in aquaculture. I can only find a few of these types of studies for Goldfish, but as Goldfish are essentially carp, I feel the research relating to Common Carp is able to be used as a good indication of what to expect with Goldfish fry and juveniles.

Effects of Low PH on Fish

Impaired Respiratory Function - Low pH is known to lower the blood oxygen-carrying capacity of aquatic species and cause corresponding declines in key functional performance traits such as growth.

Digestive Challenges - Low pH levels can disrupt the digestive process of goldfish fry. The acidic environment affects the activity of enzymes responsible for breaking down food in their stomachs. This can lead to poor nutrient absorption, malnutrition, and again, hinder growth.

I have noticed since using limestone to keep my water above 6.5, my juvenile Celestials’ appetites have improved markedly.

Metals Toxicity - In water with low pH, metals like aluminum can become more soluble and toxic. Goldfish fry exposed to elevated levels of aluminum can experience impaired growth, weakened immune systems, and other developmental issues.

Reduced Immune Response - Acidic conditions stress Goldfish fry and weaken their immune systems. A compromised immune response makes them more susceptible to diseases and infections, which can further hinder their growth and overall health.

Fry seem to be much more sensitive to water quality than adult fish. A nitrate level of 30 ppm (parts per million) is deemed to be safe for adult fish, but young fry start showing buoyancy issues at 5 ppm, as I have experienced.

Disturbed Ion Balance - Goldfish fry need a balance of ions like calcium and magnesium in the water for healthy growth and bone development. Low pH conditions can disrupt this ion balance, potentially leading to deformities, stunted growth, and fragile bones.

Ideal pH Level

The ideal range usually given for fish culture is 6.5-9.0, but this is a very wide range, and we know from a study by the Fish and Fisheries Laboratory, Zoology Department, Faculty of Science, Shahrekord University, Shahrekord – IRAN, that a pH of 9.0 killed 18cm carp after 14 days and at 6.5 the survival rate was 11%.

Why the survival rate was so low at 6.5 I can’t fathom, as this is within the accepted range for fish aquaculture. The study didn’t say when the majority of fish died, right at the beginning of the experiment or throughout it.

The research undertaken was to test at what pH, ranging from 6.0 to 9.0, did carp grow best over a 21 day period.

The research showed that the carp had the greatest weight gain and growth at a pH of 7.5-8.00.
On either side of this range, growth and weight gain fell away sharply.


For those of us breeding our fish, to ensure optimal growth and development of our fry it's crucial to maintain pH, KH and GH levels within the recommended ranges.

This is really only a problem for those of us with very soft tap water that has zero KH and very little GH, a problem more common than you would expect.

Comments? Ideas? Feedback? I'd love to hear from you. Just reply to this e-zine and tell me what you think, or what topics you want to be covered.

Next Month's Topic

Compatibility with other species

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