Water Testing

We test water using a colourmetric system.  This mean that we use tablets (chemical reagents) that change the sample to prescribed colour which is then read against a standard colour disc.  The only test that does not do this is Total Alkalinity.

 NB: The chemical agents used in test kits can be irritants.  Do not handle with bare hands.  Ensure used samples are flush down the drain and ensure hands are washed after handling.

Operational Notes

Chlorine

 Currently the sealion and penguin exhibits use chlorine to achieve two desired results:

(1) To disinfect the water to ensure there is not a proliferation of harmful pathogens (disease causing organisms) such as bacteria and virus;

(2) To oxidize pollutants such as ammonia which are produced by the animals as a by-product of the metabolic processes, e.g. using food for body growth, repair and energy. 

The chlorination of water is complex.  This is made more problematic when it is added to contaminated (polluted) waters as found in our animal exhibits.   Unfortunately, you cannot just add chlorine and then quantify a reading as chlorine can be found in various different types depending on the type of water it is added to.

Types of Chlorine

Simplistically there exist two types of chlorine:

Free Chlorine:  This is a highly effective disinfectant and oxidiser that is non-toxic and non-irritating at many milligrams per litre (mg/L).  It is the most desired type of chlorine that needs to be found in reasonable amounts for the effective chlorinated of pool systems.

Combined Chlorine:  As the name suggests this is free chlorine that has become combined with other chemicals in the water, e.g. ammonia.  Combined chlorine is made up of various species of chloramines that are to a greater of less degree both less effective as a disinfectant unlike free chlorine and presence is also likely to irritate or burn swimming animals. 

To complicate matter further, when chlorine is added to polluted water it will very quickly becomes combined chlorine.  However, fortunately, if chlorine is continually added in the right amounts a second reaction occurs sometimes referred to as the “break point” with the increasing free chlorine suppressing the combined chlorine and this chlorine type becoming the predominate chlorine in the pool. See Table 1.

Table 1: Example of a typical reaction to chlorine in polluted water

 

Normally, the ratio of free to combined chlorine should be at least 2:1 or 3:1, e.g. Free: 1.0 Combined: 0.5 or Free: 0.6 Combined: 0.2.

This is, of course, a very simplistic explanation.  There is, for example, a recognised animal to water ratio for chlorination (approximately 100 tones - 22, 000 gallons - of pool water per sea-lion), which if exceeded, i.e. too many animals in too little water, the above situation in Table 1 will not take place and combine chlorines will always predominate and, in fact, will reach dangerous levels regardless how much chlorine you add to the pool. 

Nonetheless, this basic understanding of this process should aid understanding as to why it is sometimes logical to add more chlorine to a pool when animals may appear to display irritation from combined chlorine.

NB: The chlorine test first thing in the morning is the most important.  This will give you reasonable idea of how well the system is performing.  Chlorine levels will drop during the day.  Moreover, when the pool is exposed to bright sunlight, which will remove chlorine from the water.  Do not adjust the chlorine pump based on midday and afternoon readings as this could result is very higher chlorine reading the following morning.

pH

Simply put pH is the amount of acid or alkalinity in water on a range from 1 to 14 with 7 being neutral. See Table 2.

 Table 2. pH values and what they mean.

 

Free chlorine is more effective at pH towards neutral so it should be maintained at around 7.4 to 7.6.  The pH is controlled by the addition of hydrochloric acid from a metered dosage pump.

Total Alkalinity (M)

This is a measurement of the amount of certain calcium salts, e.g. calcium carbonate (CaCO₃) in the water and related directly to the pH level and, to a lesser extent, hardness or softness of water.  It is sometimes called a “buffer” it helps balance the pH value.  We are aiming for a Total Alkalinity no more than 140 mg/L and no less than 100 mg/L.  This should ensure that the pH range will hold around the desired level of 7.4 – 7.6.  Once again, the level is control by the dosage of hydrochloric acid.

NB: Both liquid chlorine and the mains water at Chessington are alkaline by nature and, by default, will have the effect of raising the alkalinity and pH of the pool water.  This is one reason we have to use a low background does of acid to compensate.

Aluminium Sulphate

After the backwashing of the sand filters we normally add approximately 1 kg of aluminium sulphate.  This aids the filtration process by flocculation, a process where small particles are attracted together and thus become bigger and easier for the filters to remove, and thus improve water quality.  Note: aluminium sulphate does not remove combined chlorine. 

NB: This chemical is safe in the above stated amount.  However, it should not be excessively used as it can passed through the filter systems and accumulate in the pools and can, at levels of 0.3 mg/L, be an irritant to animals eyes.

TROUBLE SHOOTING: WHAT IF?

Q: The pH has now dropped to 7.0.

A: Check the Total Alkalinity.  If it remains at 100 mg/L or above the pH should start to rise over the next day or so.  However, if the Total Alkalinity is under 100 mg/L switch the acid pump off.  Leave pool for 24 hours and re-test.  If the Total Alkalinity is now above 100 mg/L switch the acid pump back on.    If not, do a major backwash on the filter system and replace some of the pool water with mains water.  NB: too much suppression or lowering of the pH suggests the pumps dosing level may need to be recalibrated (turned down).

Q: The pH has become greater than 7.8.

A: Check the Total Alkalinity.  If it remains at 100 mg/L or above the pH should start to rise over the next day or so.  However, if the Total Alkalinity is not between 100 mg/L - 140mg/L turn up the acid pump.  Leave pool for 24 hours and re-test.  Continue to monitor of the following days and careful adjust the dosage on the acid pump until the levels are stable. NB: check that the acid pump is actually working and that you have not run out of acid.

Q:  The Combined Chlorine is higher than the Free Chlorine.

A:  Backwash the filter system and add mains water.  Turn up the chlorine pump.  Check chlorine levels every hour until Free Chlorine levels have become greater than the Combines.  Re adjust the chlorine pump settings.

Q: The Free Chlorine reading is over 2.0 mg/L this morning.

A: What is the Combined Chlorine?  If it is low, e.g. less than 0.5, do a second test two hours later.  If the level still remains high switch the chlorine pump off until the level drops.  Re-adjust the pump to a lower dosage.

Q: The filter pumps have failed and we have no filtration.  Should be continue to dose chlorine and acid?

A: No.  This would result in clouds of chemical hanging in the water column which animals could swim through and be irritated or burned by.  Inform engineering to get the fault diagnosed and fixed.  NB: be aware that if the filtration is off for several days there will be an accumulation of animal pollution that will cause several days of imbalance in the pool readings when the filter plant is finally back in operation.