For example, certain small cichlids and loaches love to burrow

Right now I have gravel but I am thinking about using sand in new tank
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With gravel or sand, you will have to decide how much to get. The recommendation is 2 inches of gravel for tanks up to 55 gallons, and 3 to 4 inches for larger aquariums. With sand, you want to have 1 inch of sand for tanks with small burrowing fish and 2 inches for larger burrowing fish. A good guideline for most tanks is to purchase 1.5 pounds of substrate per gallon. However, this guideline is inaccurate for tall or unusually shaped aquariums. Resort to trial and error if necessarily.
So I've got to set up my new 25 gallon high planted tank for Angelfish. I have been debating a substrate like Fluval stratum, traditional gravel, or maybe sand?
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When doing water changes, I have a habit of stirring up the sand or gravel very thoroughly, with the reasoning being three-fold: I have read that some aquarists disagree with this strategy, arguing that it kills the beneficial bacteria in the gravel, and may lead to an ammonia or nitrite spike for the fish in the tank; I've also heard that by releasing potentially toxic gases, it risks poisoning the fishes. Jun 9, 2016 - Aquarium substrate is the layer to cover the bottom of a fish tank. It can be gravel, sand, crushed coral, or other forms of substances.
Photo provided by Flickr63 Items - Browse the latest aquarium gravel, seashells, decorative stones and sand options for your fish tank. Give your aquarium a whole new look.
Photo provided by FlickrAquarium Advice - Gravel or Sand? by Pondguru - YouTube
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Two inches is a typical recommendation, with fish-keepers using a range of 1" to 2.5" for a fish-only tank. For a planted tank, you'll need an additional 1" nutrient layer below the sand or gravel, as described below in this FAQ.So with fish like catfish and spiny eels -- not tomention loaches, mormyrids, gobies, earth-eating cichlids, andfreshwater flatfish -- you really want to keep them in a tank with asofter substrate than gravel. Sand is an easy to use option, butaquarists do need to bear in mind that there are at least threedifferent types they are likely to encounter. Each has its uses, butbecause of their very different chemical properties they are not allequally suitable for any given aquarium. The material that sits in the bottom of an aquarium is called substrate. There are several different choices for aquarium substrate, the most common of which are sand and gravel. While sand and gravel might seem quite similar, each one has its benefits and drawbacks. Deciding which one to use depends on the types of fish you are going to keep in your tank as well as some other considerations. Our guide will help you decide which is best for your aquarium.Some plants and animals you may keep in your aquarium have strong preferences for either sand or gravel substrate. For example, many species of cichlids need sand substrate in order to thrive since eating particles of sand help them digest food. Goldfish, on the other hand, risk suffering from an intestinal blockage if they accidentally ingest sand and so should always be housed in gravel substrate. Aquarium plants also have preferences for sand or gravel, so make sure to research the needs of the plants and animals in your tank before committing to sand or gravel.On the other hand, river sand cannot be used withan undergravel filter; unlike coral sand the grains are so small andcompact so readily that it cannot be separated from a gravel filter bedwithout impeding the flow of water. River sand can only be used as adecorative medium for covering the bottom of the tank, and in anunplanted tank the depth should be no greater than that which the fishcan easily move around while they're digging. The danger comes fromfood or other pieces of organic matter getting buried in the sand andallowed to decay anaerobically. Anaerobic decay is bad because itproduces toxic gases that can leak into the aquarium stressing, andpotentially killing, the fish. It is usually recommended thatsubstrates that are not part of an undergravel filter should be nodeeper than around 1 to 2 cm. Planted tanks can get away with greaterdepths, because the roots themselves will oxygenate the substratepreventing the risk of anaerobic decay, and where you are keeping bigfish, such as violet gobies or flounders, that can and do shift largequantities of sand, you can increase the depth of sand used accordingto the size of the fish in question. Basically I always advise using sand in a tropical aquarium and never use the bright coloured gravel unless for goldfish (and it looks shocking in a tropical tank).