FAQ: Tank Decor for fish

Hard green spots on rocks and glass are usually green spot algae, favoured by long or strong lighting and slow-growing plants. Scrape them off, shorten the light period and keep algae-eating snails.

Yes, nerite snails, shrimp and some catfish keep grazing algae and biofilm off rocks, wood and decor. They do not replace regular care, but they greatly reduce how often decorations need taking out and cleaning.

After an illness, scrub the decor and scald it with hot water, or let it dry out completely for a few days, as many pathogens cannot survive without water. For a specific illness and how to prepare the tank, ask a vet.

Put the largest decorations, rocks and roots at the back or sides and lower ones at the front, leaving open swimming space in the middle. Arranging decor asymmetrically around one or two focal points makes the tank look more natural.

The golden ratio, or rule of thirds, suggests placing the main rock or root not in the centre but about a third of the tank’s length from one end. Such an arrangement looks more balanced and natural to the eye than a symmetrical one.

Substrate that slopes up towards the back, smaller rocks at the front and larger ones behind, a dark background and taller plants at the rear all create depth. A path or ‘sand river’ between the decor also draws the eye into the tank.

Pour a deeper layer at the back and a thinner one at the front, and to stop it sliding, hold terraces in place with rocks or substrate dividers. Over time substrate tends to level out, especially if the fish dig.

Hardscape is the aquarium’s framework of rocks, wood and substrate before any plants go in. A well-planned hardscape shapes the whole layout, so it is worth trying it out dry before adding water.

Yes, but do it carefully and in stages so you do not stir up the substrate or frighten the fish. For territorial fish such as cichlids, rearranging can even help, as it breaks up established territories and reduces aggression.

Yes, large rocks and roots can create dead spots where debris collects, or direct the flow onto the fish. Arrange the decor so water circulates freely around the whole tank, especially near the bottom.

Yes, rocks, roots, substrate and a 3D background displace water, so the real water volume can be a tenth or more below the tank’s stated capacity. Bear that in mind when dosing water treatments and deciding stocking.

The filter and heater can be hidden behind tall rocks, roots or a 3D background, with a gap left for water flow. The heater must not touch the decor or substrate, and the filter intake must stay clear.

Measure the tank’s inside dimensions, decide which fish it is for and choose a style. Plan the decor around the fishes’ needs, the weight the stand can bear and open swimming space, and lay out rocks and wood dry before filling.

It is not required, but a tank looks more cohesive with one type of rock and one kind of wood. A mix of rocks in different colours and textures often looks random, while a consistent style gives the impression of a natural habitat.

In a biotope tank the decor, substrate, plants and fish reproduce one specific natural habitat, such as an Amazon creek with sand, roots and leaves, or a rocky Lake Malawi shoreline. Start from descriptions and photos of the place you have chosen.

Decor that breaks lines of sight between fish and creates several separate territories with hides reduces aggression. Rock piles, roots and dense plants let weaker fish get out of a dominant fish’s view.

Rinse the new decoration, make sure it does not affect the water, and lower it in slowly so you do not stir up the substrate. Set large rocks on the bottom glass, carefully moving the substrate aside so no fish are underneath and the rocks cannot topple.

A tank’s weight is the water (about 1 kg per litre), substrate, rocks, glass and equipment. Rocks can weigh tens of kilograms, so make sure the stand and floor can bear the total, and spread heavy rocks evenly.

Leftover food collects under rocks and decor when they sit on the substrate and leave still corners between them. Set large rocks on the bottom glass, leave gaps for flow, do not overfeed, and now and then lift or turn light decorations to siphon out the debris beneath.

Limy rocks, shells, coral and aragonite raise hardness and pH, while wood, leaves and cones lower them slightly. Granite, quartz, slate, lava rock and artificial decor usually leave the water unchanged.