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The Goldfish Gazette, Issue #110 Aquarium Substrate
February 27, 2023

Goldfish Care Tips

A Free Monthly Resource For Goldfish Enthusiasts
February 2023
Issue #110

In This Issue
Aquarium Substrate

Aquarium substrate is used to beautify the aquarium aquascape, provide plant anchorage, and can be used as a filtering medium, but there can also be downsides.

Aquarium Substrate

Light colored substrate causes colors to fade

The question "what is the best substrate to use in a Goldfish aquarium" often comes up in Goldfish social media groups. The three options discussed are whether to use sand, gravel, or nothing.

All three have their advantages and problems.

Gravel Substrate

Choking on Gravel

I have read on a reputable website that fish can’t choke and I quote “First off fish can’t “choke”. They breath (sic) through gills which cannot be obstructed by a grain of gravel.”

The logic is sound and the author gives other possibilities that can make it appear the fish has choked. He often asks on social media whether the owner found gravel in the gullet, and invariably they didn’t look.

I can categorically tell you that Goldfish CAN and DO choke on gravel. I have lost two this way, and yes, a piece of smooth round gravel was stuck in the gullet of each.

The trap I fell into was the fish grew, so gravel that was too large for them to suck up into their mouths 3 months earlier, then became small enough.

Why they died I can only speculate. It was either from restricted water flow across the gills, stress, or both.

Color Selection

Many aquarists choose white gravel for their aquarium. This color can look quite impressive, but fish react to it by lowering their color intensity to try and match their background. Darker colored gravel has the opposite effect.

Gravel Size

Aside from the choking danger, gravel above 4mm (3/16”) in diameter allows food to get caught between the substrate and out of reach of the fish. It then rots adding extra bio-load to the filter system.

The bigger the size of the gravel, the bigger the problem. Using marbles as substrate is an extreme example of what not to do.

Sand Substrate

Goldfish will never choke on sand substrate, and food doesn’t get lost between the particles, which is why many Goldfish keepers use it.

The same conditions apply for color choice as they do for gravel. Choose light-colored sand and your fish’s color intensity will fade.

Sand size is important if you plan to install under-substrate filters, as the smaller the sand particle diameter, the less efficient the filters become.

If you are going to use sand as a substrate, be aware that very fine sand can cause accelerated pump wear in filters with water pumps such as canister and HOB (hang on back) filters.

Bare Aquarium

An aquarium with no substrate will never look as good as one with substrate. However, a bare aquarium is very easy to maintain.

Water changes are simple as you don’t have to worry about sucking up substrate with the siphon, and there is no substrate to have to clean.

Plants can be grown in containers and other decorations added if desired.

If your bare aquarium is sitting on a sheet of white polystyrene, as it should be to prevent glass breakage, place something dark-colored between the polystyrene and the aquarium base.


Adding substrate or not to your aquarium is a matter of personal choice, but if you do, you need to take into consideration fish size in relation to substrate size, whether you plan to add live plants, and if you are installing an under-substrate filter.

I will go into more detail about these often maligned filters next month.

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

Under-substrate filters

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