Substrate is one of the most highly debated topics among the goldfish world. Just like their wild carp ancestors, we often find our goldies relentlessly sifting through the substrate in hopes of uncovering a hidden treat. Because of this natural foraging behavior, the choice of substrate is essential in ensuring your goldfish are able to live a long, healthy life. But what exactly IS the “right” substrate for our goldfish? This blog will discuss the pros and cons of a few different substrates on the market, to help you decide what will be best for your finned friends. Pea sized gravel: Gravel is, by far, the most popular substrate used in aquariums throughout the world. These attractive little stones can be found in almost any color, texture, shape and size. Gravel 2-3mm in diameter, or “pea-sized”, is sought after for its ability to hide debris, large amount of surface area to house beneficial bacteria, and allow water flow to plant roots. Not to mention pea gravel is highly available and extremely inexpensive.

It seems like the perfect substrate for goldfish... right? Despite the benefits, gravel may not actually be the best choice of substrate for goldfish. Gravel easily traps waste, and even with a gravel vacuum, its quite difficult to prevent a buildup of toxins at the bottom of the tank. This, coupled with the fact that goldfish are massive waste producers and enjoy rummaging around the bottom, can have disastrous consequences. fish tank filter south africaLong term exposure to these toxins can weaken the fish’s immune system and leave them susceptible to bacterial infections. fish tank gravel cleaner vacuumIn addition, ingestion of gravel becomes a real threat as the goldfish grow. fish tank heater asda

One or two swallowed rocks can lead to impaction or a rupture in the digestive tract. If this occurs, there isn’t much hope that the goldfish will recover. So, while young goldfish may kept on pea gravel with diligent maintenance, this substrate becomes less and less practical for longstanding goldfish owners. Fine gravel: Using fine grained gravel offers a solution to one of the major issues associated with this type of substrate. Large pebbles easily trap detritus and act as a breeding ground for harmful bacteria. Smaller gravel tends to be much easier to clean, preventing a buildup of waste. However, even fine grained gravel can prove to be dangerous to our goldfish. If consumed, this substrate can also cause major damage to the intestinal tract. Pool Filter/Play Sand: This type of sand, undoubtedly, is the superior choice of substrate for goldfish tanks. While it may not be as colorful as most other substrates, it gives the aquarium a very natural feel. Many sources claim that sand can cause irritations to the fish’s gills, but this statement has since been disproved.

The goldfish’s wild cousins lived in muddy, sandy streams with few large rocks. Their gill covers are not as delicate as they seem, and goldfish are actually very well adapted to sand. In fact, ingesting small amounts of sand may even be beneficial to the fish, as it helps to clear out the digestive tract. It certainly can’t harm them, and goldfish seem to really enjoy digging around in it. Using sand in a goldfish tank also helps with water quality, as all the waste sits on the surface, making it very simple to vacuum up. When rinsed very well prior to use in the aquarium, all of the dust and light particles can be removed, leaving a dense substrate that won’t cloud the water, even with the constant sifting from goldfish. In addition, one benefit of keeping sand that is often overlooked, is the use of deep sand beds. This is achieved when the sand is allowed to develop pockets of anaerobic bacteria deep within the substrate (at least 3 inches below the surface). This bacteria is renowned for its benefit to rooting plants, providing them with a steady source of nutrients.

However, the biggest advantage gained from deep sand beds in goldfish tanks, is its ability to quickly and efficiently consume nitrates in the water. When housing such messy fish, any amount of nitrate reduction is extremely beneficial. Lastly, play and pool filter sand is even less costly than gravel, with Quickrette play sand ranging from $2-5 per 50lb bag. With its natural appearance, availability, low price and profitability in the aquarium, what’s there not to love about sand? Black or White Sand: Colored sands may seem more attractive than natural colored sand, it tends to make waste much more noticeable on the surface. Many people don’t mind this, but it is a trade-off that should be considered. This substrate takes the title for least expensive on the list. Its actually “dirt” cheap! Soil is often used in planted aquariums, as it can easily sustain rooted plants without any additional fertilizers. But, even when capped with gravel or sand, soil can be very “dirty” (I crack myself up).

With the reckless nature of foraging goldfish digging through the substrate, this can lead to a very messy tank, without much benefit to the plants or fish. In most cases, dirt is best left in the yard rather than the goldfish tank. While they may look nice as a substrate, marbles provide no real benefit to goldfish or the tank. They generally aren’t extremely cheap, nor are they easy to clean. Marbles are notorious for trapping loads of waste, giving the tank quite a messy look after some time. Adult goldfish may also choke on smaller marbles in their attempt to find food stuck between the substrate. These also make plant keeping nearly impossible. Overall, a poor choice for goldfish tanks. A common remedy for low hardness or alkalinity in a tank is to use crushed shells and/or crushed coral as a substrate. While hard water provides benefit to goldfish fins and scales, this type of substrate can cause major damage to the fish’s mouth and intestines if ingested. Crushed shells and coral substrate is very course, and sometimes even sharp.

Curious goldfish can become seriously injured from digging around it, and the effects are even more concerning if the fish is allowed to swallow the substrate. Crushed shells and coral are best placed in the filter, instead of on the bottom of a goldfish tank. River rocks are best used sporadically as decorations in the tank, and not as a complete substrate. There is no risk of goldfish swallowing these large stones, but they are absolutely horrid to clean around. For those who are less concerned about aesthetics, tanks without any substrate at all can lead to the most healthy goldfish. Breeders use bare bottom tanks to keep water quality pristine, and prevent any injury that could be caused from the goldfish snagging fins or ingesting the substrate. Live plants are limited when using a bare bottom tank, but most floating goldfish-proof plants will be suitable, as well as plants tied on to large stones or driftwood. Some goldfish owners even use small pots or jars to house a few live plants within the tank.