Fish, Tanks and Ponds

Fish, Tanks and Ponds
A comprehensive guide to fish

Aquarium decor

Fundulopanchax gardneri


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.


Plain gravel.

Probably the most common substrate used but care should still be taken when choosing it.
Make sure it isn't to 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 to easily and plants find it easy to root in.
Make sure the gravel doesn't contain any calcareous material like limestone, shells, coral fragments ect 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 too 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.

Silica Sand.

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 to deep and that will lead to problems.
It can be used below gravel and when used this way it makes a great place for plants to root.
The sand is very pale and if used in a sparsely decorated tank with bright lighting it will make the fish look washed out.

River Sand.

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.

Coral Sand.

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 their best.
It will alter the waters 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, Apistogramma 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 mess.
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.

Substrate additives

Mainly used to feed plants or to help maintain the water chemistry.

Calcium plus

Helps maintain a high pH.


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.


Used like fluorite, many people I know have said it is better and cleaner to use.

Rocks and Stones

There are a lot of stones to avoid in the fish tank, these include - Ores (rocks containing metal), 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.

Lime Stone.

To heavy and will raise the pH, not recommended.


Varies in shades of golden brown and 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 ect.

Tuffa Rock.

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 it 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.

Dead Coral.

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.

Live Rock.

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

Volcanic Rock.

Completely inert.
Very light.
Needs to be mixed with rounded stones because it is to rough for fish to use for spawning.
It has an unnatural purple colour when new, but it soon naturalises.


Cobbles come in various sizes and can be purchased from garden centres usually for far less than a fish shop would sell them for.

Cobbles are safe to use but can be quite heavy, but cobbles do look very natural, being well rounded they look water worn.

Some of the best rift valley aquarium set ups that I have seen have all used cobbles as the main decor.

All stones

If a stone of any sort has veins of metal running through it or if what appears to be rust spots on its surface then it is probably best avoided. Heavy metals can be quite toxic to fishes and it isn't worth the risk.



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 beginning.

Mopani wood.

One of the hardest most dense woods in nature.
Will sink like a stone un-aided.
It will initially colour the water but it wont affect the water chemistry greatly.
It is naturally very gnarly and it has dark and pale streaks running through it.
Can be expensive.

Green wood.

Not recommended
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.

Artificial Wood.

Very realistic and safe to use.
Can be limited in size.


Real Plants
Can be difficult to grow without a specialised setup, the effort is worth it.

Artificial Plants

There are two main types of artificial plants available, material and plastic.
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 de-chlorinator has been added. Bleach will kill the fish if it is allowed to get into the aquarium. If in doubt rinse again.

Other Items.

Terracotta Pots.
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.

Sea shells.

Marine and African Cichlid Aquaria only.
Adds a little authenticity to a marine tank.
Essential when Hermit Crabs are being cared for.
Essential for 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.

Coloured gravels.

If these are to your taste then use them. The fish won't notice in most cases.
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.

As above.


As above. These must be intended for purpose, don't use regular ornaments in a fish tank!!!


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.

Can I add this object?

When you are decorating your tank, you may come across some items that you would like to add to a tank but are uncertain if they will be safe to add. There are a few things that need to be considered before adding any piece of decoration to the tank

Changing water chemistry:

There are many items that are safe to add to an aquarium, however some things that you come across will affect the pH of your tank. In some cases this may be a desirable result while in other cases it could really play mess up your water chemistry. If an object is known to alter pH then you will need to use caution and only add that object to an aquarium where the altered pH will be a desirable result, not one that you need to fight with constantly. There is a simply test to see if an object will raise the pH of your tank called an Acid Test.
Before adding acid A simple acid test will help determine if an object will increase the pH of an aquarium. Although vinegar is most commonly recommended, it isn't a strong enough acid to be 100% accurate. If you want to be completely sure if something will raise the pH of your tank when a vinegar test fails to indicate, then boric acid is the next best thing.
Place the object you wish to test in a container.

The vinegar test

Watch the reaction carefully.

Aragonite sand

Aragonite sand with vinegar added to it.
If it begins to fizz the item you are testing has a high pH and will alter the water conditions in your tank.
There are also a few items, mainly peat, driftwood and bogwood, that will lower the pH of your water. Testing for this will be more difficult then testing to see if an item will increase your pH. one way to test the object would be to boil it in some water for a while. Test the pH of the water before you add the object and after it's been boiled for a while. If the pH of the water dropped then the item will lower the pH in your tank.

Biological Considerations:

If you collected an item from the wild, such as rocks, sand or wood that you would like to add to the tank, you are going to need to have some method of sterilizing it to avoid introducing harmful organic life or antibacterial compounds.
Green wood has natural defences to protect them from infection. These same defences will pose a threat to your biological filtration in the tank and should not be used.
Rocks, sand and wood that comes out of a lake or stream could have parasites, bacteria, algae, or predators hiding within it. Without sterilizing it you run the risk of introducing a disease that your fish inhabitants have natural defences from.

Heavy Metals:

Under no circumstances is it safe to add objects that contain heavy metals. They are extremely toxic to fish, inverts and bacteria. It is this toxicity that makes copper such an effective medication in an aquarium.

Soaps and Residues:

We have been trained from a very young age the importance of being clean and washing up after ourselves. However the soap that we use is extremely harmful to aquatic life. If an object has been cleaned using soap and water, it can not be used in an aquarium. We shouldn't even wash our hands with soap before putting them into our tank. It's best to clean an object in warm to hot water, avoiding soap altogether.

Soap will:

leave a residue on any object cleaned with it
will increase the surface tension of the water hindering gas exchange
contains a lot of phosphates that will feed algae
harm the biological filtration in the tank.


Another common substance used to clean and disinfect objects is common household bleach. Regular bleach has chemical agents that leave a residue on any surface it comes into contact with. If it is used, then you need to insure that all that residue is removed before it is used in a tank. This can be done by thoroughly rinsing the objects in warm water and using a dechlorinator to neutralize the toxic chlorine.

Sterilizing items:

Once you have an object that you would like to add to the tank and have determined it is safe for your purposes there are many ways in which you can prepare it for use in your tank. These are some safe methods:
Boil them for at least ten minutes
Bake larger items in an oven set to 350degrees F for 0.5 to 1 hour
Soak the in potassium permanganate
Leave them dry out for a couple weeks (preferably in the warm sun).