Sand, gravel, soil or en­riched clay – what’s the best choice of sub­strate for your tank and your fish?

Practical Fishkeeping (UK) - - Contents - NEALE MONKS Neale is an aquat­ics author with a pas­sion for brack­ish wa­ter species.

From sil­ica sand to aquatic soil, what’s the best type of sub­strate for your plants and your live­stock?

CHOOS­ING THE right sub­strate is one of the most im­por­tant de­ci­sions to make when set­ting up a new aquar­ium. There are so many op­tions avail­able that it’s easy to end up with the wrong kind or, at least, one that doesn’t work out quite as well as you’d hoped. Re­plac­ing sub­strate is an ex­pen­sive and time-con­sum­ing process, so it’s some­thing you’ll want to get right from the off.

In some cases, the choice of sub­strate comes down to per­sonal taste, but of­ten, the best one for the job re­ally de­pends on what fish you’d like to keep or which plants you’re try­ing to grow.


Leav­ing the tank bare is a good op­tion for tanks where clean­li­ness is the num­ber one pri­or­ity. This in­cludes breed­ing tanks, hos­pi­tal tanks and quar­an­tine tanks.


Fae­ces and de­cay­ing or­ganic mat­ter are eas­ily sy­phoned out dur­ing wa­ter changes. Med­i­ca­tions cir­cu­late around the aquar­ium more ef­fec­tively, mak­ing it harder for pathogens to sur­vive.


Looks unattrac­tive. There’s noth­ing to shore up rock­work or piles of bog­wood, so you need to use self-sup­port­ing or­na­ments and caves, such as flow­er­pots. There’s noth­ing for plants to root them­selves into, so you’re lim­ited to ar­ti­fi­cial plants, float­ing plants, or epi­phytic plants at­tached to bog­wood or rocks. Over­head light will re­flect up­wards off the glass bot­tom, stress­ing the fish and caus­ing them to ex­hibit sub­dued or washed-out colours to try to blend in.


For decades this was the de­fault choice, usu­ally on top of an un­der-gravel fil­ter plate, where the gravel acted as the bi­o­log­i­cal medium. While still a pop­u­lar choice (and rarely a bad one), think about the al­ter­na­tives be­fore go­ing down this route as plain gravel does have some short­com­ings.


Cheap and eas­ily ob­tained. Lime-free gravel from aquat­ics shops is chem­i­cally in­ert, so it won’t change the ph or wa­ter hard­ness. Nu­mer­ous grades avail­able, from fine pea gravel ideal for small fish com­mu­ni­ties, to al­most peb­bly grav­els less eas­ily dis­turbed by jumbo species. Its dark colour min­imises up­welling light, en­hanc­ing the colours of your fish.


Scratches and short­ens the whiskers of cat­fish and loaches as they forage for food. Sharper grades of gravel may cause so much dam­age that the fish be­come prone to bac­te­rial in­fec­tions. While stir­ring the gravel helps when clean­ing out dirt and de­bris, plant roots will make it harder to do this prop­erly. It’s de­void of min­eral nu­tri­ents, so pro­vides lit­tle ben­e­fit to plants be­yond an­chor­age.


These are usu­ally smooth grav­els that are painted and then cov­ered with an aquar­ium-safe var­nish. While not to ev­ery­one’s taste, they’re of­ten pop­u­lar with chil­dren.


Lots of colours to choose from. Darker grav­els, par­tic­u­larly black, can high­light cer­tain fishes’ colours. Chem­i­cally in­ert, so won’t change the ph or hard­ness of the wa­ter.


Un­nat­u­ral in ap­pear­ance – and can look a bit naff! Brighter colours, par­tic­u­larly white, re­flect light up­wards, which can stress fish and cause them to ex­hibit sub­dued coloura­tion. Fish with del­i­cate colours look dull next to red, blue and other vivid grav­els. Don’t con­tain min­eral nu­tri­ents for plants. Pricier than plain gravel.


This lime-free sand is chem­i­cally in­ert and widely used by gar­den­ers. There are two types avail­able – sharp sand and smooth (or sil­ver) sand. Don’t use sharp sand as it will scratch bot­tom-dwelling fish like loaches and cat­fish, but sil­ver sand can work very well if cleaned thor­oughly be­fore use.

Sil­ver sand is also mar­keted as pool fil­ter sand, which is usu­ally much cleaner than the smooth sand sold by gar­den cen­tres.


In­ex­pen­sive and easy to ob­tain. Makes a fab­u­lous sub­strate for tanks with cat­fish, loaches, and other bur­row­ing or dig­ging species. Nat­u­ral in ap­pear­ance, and a great choice for biotope tanks. Won’t cause a change in the ph or hard­ness of the wa­ter. Set up cor­rectly, deep sand beds be­come par­tially anaer­o­bic, fos­ter­ing the growth of den­i­tri­fy­ing bac­te­ria that can lower ni­trate lev­els.


Con­tains lit­tle in the way of min­eral nu­tri­ents, though plants will root read­ily. It re­flects some light up­wards, so some fish will show weaker colours. Big fish can move it about, po­ten­tially un­der­min­ing rock­work. Some sand may end up in the fil­ter if the fil­ter in­let is too close to the sub­strate. Sand will scratch the tank if caught be­tween the glass and an al­gae scraper.


Some are ar­ti­fi­cial, some nat­u­ral, and some are in­dus­trial by-prod­ucts. What­ever their ori­gins, they look su­perb in the right tank, of­fer­ing more va­ri­ety than plain sil­ica sand.


Usu­ally chem­i­cally in­ert – but check with the man­u­fac­turer. Var­i­ous dark shades are avail­able, in­clud­ing black vol­canic sand that can look ab­so­lutely fab­u­lous in planted aquaria, show­ing off the sub­tly coloured fish and shrimps to best ad­van­tage. Cons Dearer than plain sil­ver sand. Some are too sharp, so they aren’t suit­able for bur­row­ers like cat­fish and loaches. Some types con­tain min­eral nu­tri­ents that en­hance plant growth, but most of them don’t.


We don’t rec­om­mend you dig up your gar­den, but nat­u­ral soil prod­ucts from aquar­ium shops are use­ful for help­ing to repli­cate the sub­strates found in rain­for­est streams or pools.


Very nat­u­ral­is­tic, es­pe­cially with some Cat­appa leaves and bog­wood roots added. The dark colour en­hances many fish, es­pe­cially those with flu­o­res­cent mark­ings. Tends to tint the wa­ter over time, fur­ther en­hanc­ing colours. The tea-coloured wa­ter is par­tic­u­larly ap­pre­ci­ated by black­wa­ter habi­tat species, such as Discus. Bur­row­ing fish love it and be­have in a very nat­u­ral man­ner –

es­pe­cially ele­phant­noses and spiny eels, which don’t thrive in tanks with gravel sub­strates. Plants root quickly, as you would ex­pect.


Bet­ter in tanks with small fish. Larger fish will dis­turb the soil, mak­ing the wa­ter murky and po­ten­tially clog­ging the fil­ter in­let. Con­tains some min­eral nu­tri­ents, par­tic­u­larly iron, but this varies be­tween brands, so you might need to use ad­di­tional fer­tiliser. Quite ex­pen­sive, al­though in tanks with­out rooted plants you only need enough to cover the bot­tom glass.


This is sim­i­lar to the large pieces of ‘lava rock’ sold as dec­o­ra­tion and makes a good al­ter­na­tive to plain gravel.


Lighter than gravel. It has a por­ous struc­ture, which al­lows slow move­ment of wa­ter through the sub­strate. This cre­ates par­tially anoxic con­di­tions that fos­ter the growth of den­i­tri­fy­ing bac­te­ria, and main­te­nance of non-ox­i­dised min­eral ions that plants can use. Open struc­ture, so good for un­der-gravel fil­ters and tanks with sub­strate heaters. Rough tex­ture forms a se­cure base for se­cur­ing bog­wood and rock­work. Dark in colour, so shows off fish well. Some types in­clude min­er­als for good plant growth, though pe­ri­odic use of fer­tilis­ers may still be needed.


Rough tex­ture, which can cause dam­age to bur­row­ing fish. More ex­pen­sive than gravel.


Of­ten based on min­eral-en­riched clay, which slowly re­leases ben­e­fi­cial min­er­als around the roots of your plants. Plants are more fussed about light in­ten­sity than any­thing else though, so if your tank doesn’t have strong light­ing, a fancy sub­strate won’t make much dif­fer­ence.


The best choice for aquar­i­ums with rooted plants. Vig­or­ous plant growth is the eas­i­est way to avoid al­gae prob­lems, so plants that get their nu­tri­ents from the sub­strate, rather than from the wa­ter col­umn, will re­ally ap­pre­ci­ate this stuff – as will your tank and fish. The bet­ter brands are guar­an­teed to last for five years be­fore need­ing re­place­ment. Fine and smooth, so good for bur­row­ing fish. Dark brown, so works well against the colours of your fish.


Very ex­pen­sive, al­though this is off­set by the re­duced need for pe­ri­odic fer­tiliser dos­ing. And the bet­ter plant growth means that you won’t be re­plac­ing your plants ev­ery few months!

BE­LOW: A stark con­trast be­tween a nat­u­ral­is­tic look and colour­fully ad­ven­tur­ous.

ABOVE: The wrong sub­strate can de­stroy cat­fish whiskers.

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