Goldfish are an auspicious and incredibly attractive addition to outdoor ponds. Their fiery colors, peaceful nature, and gentle swimming behavior add value to their ornamental appeal. They thrive best in well-maintained and ecologically balanced ponds, including those that are equipped with pond pumps, high-quality filters, and water features for extra aeration. This doesn’t mean they require all of this fancy pond equipment to survive, however.
Able to persist and even dominate natural waterways as escapees, goldfish are obviously highly adaptable and vigorous. Their hardy varieties are some of the most robust and low-maintenance of all popular freshwater fish species. That being said, they do still require the bare minimum of good water conditions to survive. These include steady dissolved oxygen (DO) levels, a gentle current, low to absent levels of ammonia and nitrates, and fairly neutral pH levels.
It’s possible to create and maintain these conditions in ponds without a pump, which means that goldfish can hypothetically survive in one. The pond would have to be a relatively mature and naturalized body of water, able to cycle nutrients at desirable rates. Though goldfish can even thrive and reproduce in pumpless ponds, there are many aspects to consider before stocking them.
Main Concerns of Stocking Goldfish in Pump-Free Ponds
1) Seasonal fluctuations of DO levels
In natural ponds, dissolved oxygen levels are affected by a number of factors. These include, but are not limited to, temperature, oxygen consumption of algae and plants, the biomass of oxygen-consuming organisms in the pond, depth, light exposure, and water circulation. These pond properties are dynamic, meaning they continually change throughout the year.
One of the major dangers to stocking goldfish in pump-free ponds is the instability of dissolved oxygen levels. These rise and fall within a single day, as a response to the metabolic requirements of the pond’s microscopic to large inhabitants. DO levels invariably change with the seasons as water temperature, food availability, and precipitation levels fluctuate. This means that oxygen can be stable in winter and then dangerously low in summer.
During some months, it may be necessary to supplement DO levels in natural outdoor ponds with the use of a pump. This should help prevent goldfish from suffocating or becoming stressed. Once ambient conditions have normalized and DO levels are fairly stable, the pump can be removed once more. If you never intend to introduce a pump into your pond, make sure to stock very conservative numbers of goldfish.
2) Stagnant water
Stagnant or unmoving water is never desirable in a natural pond. Without the circulation of oxygen and nutrients, a pond can quickly become toxic. Fully stagnant ponds fail to support complex ecosystems and instead become sources of sulfates, pathogens, and pests. Their anoxic conditions would be detrimental to the lives of goldfish, which continuously need oxygen to survive.
Unfortunately, stagnant water may be a seasonal feature of outdoor ponds, especially in the absence of rain and winds. Its occurrence is made more likely by the presence of algal mats and dense colonies of floating plants. These act as a barrier between the water’s surface and the air above. These may also consume copious amounts of oxygen. By creating a flow of water, pumps generally prevent ponds from becoming stagnant. The water movement also aids in reducing the expansion of floating plant colonies, allowing more oxygen to naturally diffuse into the pond.
Stagnant pond water cannot support the needs of even the hardiest types of goldfish. They will quickly deteriorate due to the low dissolved oxygen levels and are unlikely to recover from stress unless a supplementary source of oxygen is provided. In the worst case, stressed goldfish will keep to the pond bottom, where oxygen levels would be lower than that of the surface, until they finally pass.
3) High concentrations of toxic nutrients
The aerobic component of the nitrogen cycle requires the presence of enough oxygen atoms to fully convert toxic nitrates into harmless nitrogen-based byproducts. If the lack of a pond pump leads to low DO conditions, sulfur may react with available nutrients, creating a cocktail of fermenting compounds.
These toxic compounds often lead to massive fish kills. They may also cause the pond to emit a putrid odor. Low dissolved oxygen likewise leads to lower rates of decomposition, allowing waste and decaying plant matter to fester for a longer period of time in the pond. Once the pond is filled with toxic nutrients, a massive water change or a full clean-up may be required. Note that it can be very difficult to rehabilitate a toxic pond, especially in the absence of pumps.
Mature natural ponds may have fairly high dissolved oxygen levels on average, but they may struggle to rival the maintained DO levels (usually 7+ ppm) in adequately aerated ponds. As the available oxygen levels fluctuate to lows of 5 – 6 ppm, it would be best to stock the pond with lower densities of fish. This should provide the stocked goldfish with a more secure supply of oxygen.
Compared to pumped ponds, pump-free ones are more likely to become overcrowded in the sense that any additional fish can significantly bring down oxygen levels. Ornamental and aquaculture ponds may occasionally be managed to keep up with the demands of an intensive stocking density. These are usually equipped with multiple pumps, filters, and more water features for aeration.
Tips for Raising Goldfish Without a Pump
If you do intend to cultivate a small school of goldfish in a pond without a pump, it is more likely to survive if there are many sources of oxygen, such as oxygenating plants and a fountain. Mature and ecologically balanced ponds are also more likely to support the fish’ needs.
Note that the water’s surface area and depth must be limiting factors when determining the number of goldfish to stock. Of course, medium to large ponds are more likely to support goldfish populations without a pump. Enumerated below are some important tips to review before introducing goldfish into a pump-free pond.
- Place a variety of aquatic plants in the pond. A mixture of floating, submerged, and marginal plants should help keep the water cool, increase its capacity to hold oxygen, and take up excess nutrients. These are also likely to produce oxygen as a byproduct of photosynthesis. Moreover, the submerged plant material increases the surface area on which beneficial bacteria may grow. Their colonies should aid in converting toxic nutrients into safer compounds. They should also help prevent the overgrowth of harmful algae.
- Naturalize the pond edge with rocks. Just as submerged plants can increase a pond’s surface area, an irregular and deeply pocketed pond edge can do the same.
- Diversify the pond so that the goldfish need not be fed with fish feeds. As excess fish feeds sink and decompose on the pond bottom, they consume considerable amounts of dissolved oxygen. Naturalized ponds are usually full of life, which means there should be enough natural sources of food for goldfish. They will feed on insects, plant material, tiny crustaceans and mollusks, and mats of bacteria.
- Avoid overstocking the pond. Keep in mind that your goldfish will increase in size as they become adults and that they will eventually breed. Every additional fish will consume oxygen, take up space, compete for food, and produce waste. You will need to maintain a sustainable population. This could mean having to relocate your fish’s offspring in the future.
- Do not clean the pond liner. The biofilm that develops on the liner’s surface is a key element in maintaining the ecological balance of a lined pond. This film contains microbes that are vital in breaking down decomposing matter, releasing nutrients that should aid in the growth of your aquatic plants.
- In the winter, make sure to create a hole in the ice so that gas exchange can still occur. You may also opt to use a de-icer to keep the pond surface free of ice.
Other Species to Stock With Goldfish in a Pump-Free Pond
If you find that your pump-free pond is likely to accommodate a few more fish, you may wish to diversify your pond community. Though this should help increase the complexity of the pond ecosystem as a whole, don’t forget that the additional fish will consume oxygen. This means that when oxygen is scarce, they will compete with your goldfish.
Nonetheless, adding a few peaceful species should generally be safe if their mature size is much smaller than your goldfish’s. Some types of minnows and plecos may be decent pond mates, but keep in mind that they may reproduce and overcrowd your pond. Larger species, like koi and orfes, are definitely not ideal for pump-free ponds. These are highly active species that consume a lot of oxygen.
Stocking conservatively is always recommended when it comes to any type of pond, but this piece of advice is even more important in the absence of a pond pump or a filter!