Pond water quality is what keeps your fish alive and healthy

pH is very difficult parameter to measure and control in any garden pond. It is best NOT to measure it unless you really do understand the result and what is is really telling you. pH varies during day and night

More On Water Quality ... pH and Water Hardness

What is this hardness?

When you wash your hands in water and you find it difficult to get a good lather (even using quality soaps) you are in an area where the water is naturally hard. Conversely when the water feels slimy when you wash your hands the water is called soft. Where I live some 15 kms east of Johannesburg the water is probably in between.

High levels of dissolved salts and particularly magnesium and calcium salts cause hardness in water.

There are also 2 types of hardness - permanent hardness and temporary hardness.

Water that has permanent hardness has a lot of magnesium and/or calcium SULPHATE salts as well as other salts.

Temporary hardness is due to magnesium and/or calcium CARBONATES. If you look inside your kettle you might see deposits of white or grey solids on the heating element. This is CARBONATE coming out of the water when it is boiled and this is why it is called temporary.

CARBONATE hardness is important in a pond in order to control pH.

The total of the SULPHATES and CARBONATES in water is called permanent hardness or TH for short. The amount of CARBONATES only is called temporary hardness and is referred to as CH for short. Some countries use different terminologies including DH and KH.

Total hardness (TH) is important for the good physiology of fish.

The following is what happens in a pond that has a low level of CARBONATES. During the day any plants (and this includes algae which is a plant) in the water remove this small amount of carbonate and as a result the pH of the water can climb significantly and maybe even reach a level of 9.

At this level ammonia secreted by the fish themselves is EXTREMELY poisonous to fish and your fish can die - under these conditions your fish will appear distressed, gasping for air, lying on their side, lethargic and so on.

Now if there were higher levels of CH in a pond it would be difficult for the pH to rise to 9 and it would also remain a lot more stable, which is much better for fish.

If you suspect ammonia poisoning then immediately test the water for ammonia if you have the kit. If you are unable to test or if the test proves positive start changing some of the pond water immediately (say 50%) and DO NOT feed the fish - fish can live happily without feeding for days on end. Keep changing portions of pond water until you are able to stabilise the situation. Keep measuring the ammonia levels in the water.

If you ever go to a koi show you will see water from the holding tanks being changed frequently to prevent ammonia build-up.

Think of CH as preventing pH from fluctuating widely and reaching dangerously high levels. This is good for fish and plants in a pond. That is all you need to remember.

Good levels of TH in a pond are 7 to 14 degrees

Good CH levels in ponds are 6 to 12 degrees

The only way you know if you have the correct levels is to test the water yourself by buying a suitable test kit or take a water sample to a fish outlet with these testing facilities.

If you find the hardness is too low then select a product from the shelves to correct the problem and follow the instructions carefully. Hardness can be increased by using dolomite, marble chips or crushed shells.

It is also a good idea to test your tap water to see if it is hard or soft so you can forecast what might happen over a period of time.

Acceptable Values For Pond Testing

Ammonia: Nil

Nitrite: less than 0.3 mg/litre

Nitrate: 25-100 mg/litre

pH: 7.0 - 8.0

TH: 7 14 deg TH

CH: 6 - 12 deg CH

back to previous water quality page

This web page is an extract from Tony Roocroft's "The Complete Pond Solver" ... you can read more about it at http://www.really-useful-books.com ... when you buy the book you get 12 Excel pond calculators free as well as "Water Lilies and Pond Aquatics" ebook also free.