by Andy Gordon of England, and Michelle Stuart of
Reprinted, with permission, from their web site Fishtanksandponds.net
Malawi Mbuna like this young male Labeotropheus trewavase
need a very rocky environment to feel comfortable and look their best.
Photo by Andy Gordon
Almost every tank whatever type it is needs some decoration to make it look more
pleasing and to give the livestock a more natural setting and somewhere to hide. From the
substrate up there are thousands of variations and endless possibilities available to us.
But what is safe, what looks good, what are its disadvantages - in other words what can we
use to decorate our tanks with safely?
Probably the most common substrate used, but care should still be taken when choosing it.
- Make sure it isn't too sharp, the more rounded it is the better so that any bottom
living fish like loaches or Corydoras don't end up injuring them selves on it. It
isn't uncommon to see Corydoras catfish with their barbels worn away due to rough
gravel and this will shorten their lives considerably and prevent them from breeding -
strange as it sounds because male corys use their barbels in courtship.
- The size of the gravel is important too, especially if plants are going to be grown or
an under-gravel filter is used. The best size is 1 to 2 mm, at this size it will not
compact and become anaerobic too easily, and plants find it easy to root in.
- Make sure the gravel doesn't contain any calcareous material like limestone, shells,
coral fragments etc. because these will raise the pH and hardness of the water. For most
tropical fish this would be undesirable but there are a few which prefer such conditions,
and that is why it is important to know what your fish require before buying them.
- Plain gravel has no effect on the water chemistry.
Is also very popular and makes a good substrate for keeping many bottom living fish. And
always looks fresh and clean.
- The sand is prone to become compact when it is kept too deep and that will lead to
- It can be used below gravel and when used this way it makes a great place for plants to
- The sand is very pale and if used in a sparsely decorated tank with bright lighting it
will make the fish look washed out.
Worth seeking out due to its very natural looks
- This is a great substrate because it is a little more coarse than silica sand so it is
less likely to compact and it looks great.
- It has no effect on the water chemistry.
This is only suitable for marine and hard alkaline systems.
- This substrate looks very clean and makes other decor and tank occupants stand out.
- It will buffer the water and prevent pH drop to some extent.
- Because it is so pale it could make the fish appear washed out and not show them to
- It will alter the water's chemistry by making it harder and by raising the pH.
- Finer than coral sand and maintains the pH in marine aquariums more effectively.
This is another specialist substrate. For soft acidic water tanks.
- An excellent substrate for some killifish, apistogrammas and some characins where soft
acidic water is required.
- Substrate spawning killifish will use it to breed in and the eggs can be kept in it
through a dry spell if necessary.
- If there is any turbulence the bits of peat will remain in suspension and look a
- It will affect the water chemistry by softening the water and lowering the pH.
- In time it will discolour the water making it an amber colour.
Mainly used to feed plants or to help maintain the water chemistry.
- Calcium plus - Helps maintain a high pH.
- Fluorite - A plant food additive rich in iron. Needs to be mixed with other substrate
and buried below a layer of gravel. It may discolour the water initially but do not rinse
it before use or you will shorten its effective life.
- Laterite - Used like fluorite, many people I know have said it is better and cleaner to
Rocks and Stones
There are a lot of stones to avoid in the fish tank, these include - Ores (rocks
containing metal), and Calcareous (rocks containing Calcium) shouldn't generally be used
for fresh water tanks.
Pale grey in colour, suitable for all tanks.
- Completely inert and is cheap to buy. Large thin pieces can be used as a background.
- Beware of sharp edges.
Too heavy and will raise the pH. Not recommended.
Varies in shades of golden brown. Inert.
- Water-worn pebbles of varying sizes can give a very natural look to an aquarium.
- Completely safe to use for all tanks after a simple rinse.
- Can be used to construct caves etc.
Marine and African cichlid tanks only.
- A very light rock so excellent where a lot of rock is needed for building a reef.
- Very soft and easily made into different shapes, or cut.
- It is formed from Magnesium Sulphate so it will harden the water.
- Very cheap to buy - more so if you get it from garden centres instead of fish shops.
- Safe and completely inert.
- Can be sharp and is harder than glass - making it able to scratch the glass if it is
near to it or is knocked against it.
- Doesn't look very natural.
Marine tanks only. Not Recommended
- Due to poor collection and reef destruction this is an ethically poor tank decor and
illegal in some countries.
- Realistic artificial pieces are now widely available and a much better choice.
Marine Tanks only
- Cured live rock looks great in a marine tank by making it as natural as possible.
- It can provide a very good biological filter.
- Lots of marine life will be added to the tank with it.
- Some of the above life may be undesirable
- Completely inert.
- Very light.
- Needs to be mixed with rounded stones because it is too rough for fish to use for
- It has an unnatural purple colour when new, but it soon naturalises.
- Very natural and safe to use.
- Needs to be soaked for a few weeks to become waterlogged so that it sinks.
- Very popular and widely available.
- It will colour the water initially, this can be reduced by boiling in water before use.
- Heavy enough to sink without any help.
- It will acidify the water so keep an eye on the pH when it is used, particularly at the
- One of the hardest most dense woods in nature.
- Will sink like a stone unaided.
- It will initially colour the water but it won't affect the water chemistry greatly.
- It is naturally very gnarly and it has dark and pale streaks running through it.
- Can be expensive.
- Live wood or recently chopped wood is best avoided.
- It will still contain sugars and starches, and as these breakdown the free oxygen in the
water will be reduced.
- It may also contain toxins which are the trees' natural defence.
- Very realistic and safe to use.
- Can be limited in size.
More details elsewhere
- There are two main types of artificial plants available, material and
- Both suffer from algae eventually.
- The material leaves move more realistically in the water but they aren't as robust as
the plastic ones.
- There is a whole range of very realistic looking plants available today.
- They have a very long lifetime.
To clean them periodically, simply soak them in a weak bleach and water solution for an
hour, followed by several very good rinses. Keep rinsing until there is no detectable
odour of bleach. In the final rinse let them soak in a bucket of water to which some
dechlorinator has been added. Bleach will kill the fish if it is allowed to get into the
aquarium. If in doubt rinse again.
- Don't use new terracotta - lime is added during manufacture and it will
affect the water chemistry.
- Old weathered terracotta is entirely safe after a quick rinse.
- They make excellent caves for breeding dwarf cichlids.
- Oddly, they look surprisingly natural.
Marine and African cichlid aquaria only.
- Add a little authenticity to a marine tank.
- Essential when hermit crabs are being cared for.
- Essential for when Lake Tanganyikan shell dwellers are being kept and/or bred.
- They will harden the water if there are enough present, don't use in acidic water.
- If these are to your taste then use them. The fish won't notice in most
- Popular with children.
- Captive bred fish will have been raised in vats void of any decor and a natural looking
tank will look every bit as foreign to them as a multi-coloured artificial setting.
Coloured Glass Pebbles
- Amazingly these are available for fish tanks.
- I am speechless.
- I can only imagine that a moving or flashing coloured light will frighten most fish.
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