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Final Water Temperature

by George J. Reclos

Following the other two articles in the series of water changes ( water changes and how much fresh water is in your tank) we asked ourselves what other things usually bother the hobbyist and – perhaps – don’t allow him / her to follow a regular maintenance schedule. We have already covered the issues of cleaning the rocks and sand before adding them in the tank as well as how to effectively clean that sand every now and then once in your tank.

Water changes are definitely a must and the best option when it comes to “refreshing” the water in a freshwater tank. In salt water tanks this is not so partly because of the cost of the salts but – even more important – because marine fishes do not tolerate well even minor changes in their water parameters (i.e. salinity, pH, dissolved salts, alkalinity, redox potential etc.). This is due to the fact that freshwater fish come from lakes or rivers in which rainfalls alter the physicochemical composition many times a year. In the tropics where the term “heavy rainfall” means the addition within an hour of thousands of tons of fresh water, those changes may be dramatic. Therefore those fishes have adapted themselves in tolerating changes even great ones (within limits of course). This doesn’t mean they will tolerate any kind of water since the parameters that change in the wild are always kept in a specific range but it does mean that a fluctuation of 0.5 in pH or 2-3o in GH will definitely not harm them. In contrast, marine fishes live in the ocean which is remarkably stable as far as those parameters are concerned and – for the tropical marine species – even the temperature is stable throughout the year. This is why for marine tanks, water changes play a minor role and the everyday maintenance is largely left to other forms of chemical filtration like skimming and ozonizers (among others).

In conclusion, every freshwater hobbyist should have a schedule for water changes and follow it as strictly as possible. Water changes play a key role in removing the end products of all biochemical reactions that take place in our tanks and most notably (although not only) the nitrogen cycle, whose end product (nitrates) has to be removed from the water at regular, short intervals. Keeping the intervals as short as possible makes a lot of sense since this will not allow the nitrates to sky rocket so the new water will not differ dramatically from the one changed. It is not rare to suffer heavy fish losses after a large water change if the water has left in the tank for months. In our experience, water changes should be made at least twice per month and the water changed should be at least 25% every time. Weekly water changes of 30% or more will only make your fish happier and keep them healthier. There are some exceptions to this rule both ways. Thus, Tanganyika cichlids should have less water changed (15-20%) while discus would be happy with daily changes of 90% of their water. All the same, the above recommendation is valid for the vast majority of freshwater species.

The usual way to make water changes is with conditioned, pre-heated water which should be added slowly in the tank. This, usually, requires the use of (many) buckets and a great deal of work. Although this may serve small tanks it becomes really annoying when the volume of the water to be changed climbs to hundreds of liters per week. An alternative is to use tap water, directly from the tap and a garden hose. This will eliminate the need for buckets (and spills on the floor or – even worse – carpets) and will significantly reduce the time it takes to make a water change. Furthermore, you will not be tired after that and you might decide to introduce a new maintenance schedule with larger and more frequent water changes.

Pre conditioning is not an option in this case but conditioning while the water is added is also a good option which has worked for me very well over the years. First, you have to decide / calculate the volume of the water to be changed. For those using the metric system nothing is easier. You will draw a mark on the glass of you tank (the water level before the water change – AFTER adding some water to compensate for the evaporated water) and then you remove the water (again with a garden hose). You take a ruler and you calculate the height difference (ΔH). You multiply this height by the length (L) and depth (D) of your tank (in cm) and you divide by 1000 – this is the volume in liters of the water to be added to reach the same level in your tank.

Thus: (ΔH x L x D)/1000 = liters of water to be added.

You can now calculate the quantity of conditioner needed for this volume of water and then you add one third of that quantity before you start adding fresh water. When you have already added one third of water you add one more third of conditioner and you repeat the procedure till all the water has been added. Adding a 10% surplus of conditioner is always a good practice since water companies are not very fanatic when it comes to the addition of a standard amount of chlorine / chloramines in the water we drink. Indeed, in warm climates, the amount of chlorine added during the warm season is significantly more.

One major issue however is the temperature fluctuations observed when new water is added, especially when it comes directly from the tap. In winter months, tap water may have a temperature of as low as 10oC while in summer months this may climb to 26oC. In my experience, a temperature drop by 2-3oC (from 26oC to 23oC) is safe (for the species I keep anyway). However, it would be nice to know what the final water temperature will be before you start the water change otherwise you may have to stop mid-way and allow time for the heaters to warm the water in the tank before going on. This is not convenient and we are trying to make things easier for us, not more difficult.

So the issue is : What will be the final water temperature following a water change with tap (ambient temperature) water ?

You (obviously) need to know the following :

  1. What is the temperature of the water in the tank before you start the water change.
  2. What is the temperature of the tap water.
  3. What is the percentage of water you are going to change (e.g. 30%)

 You can now start Excel and create the following table in a new file (you should start at cell A1).

final temperature of your tank water

input

 

 

 

 

 

 

How many liters / gallons of water are there in your tank ?

 

Lts / Gals

V1

What is the water temperature in your tank ?

 

oC / oF

T1

What is the percentage of water you are going to change ?

 

%

X

What is the temperature of the tap water you have (number only)?

 

oC / oF

T2

 

 

 

 

The final temperature of your water will be

 

oC/oF

T3

Please note that all temperatures should be in either Celsius or Fahrenheit and all volumes in either liters or gallons.

In B3 you just type the volume (in liters or gallons) of your tank (better still the actual water volume if you can get a good estimation of it) – just type the number.

In B4 you just type the temperature of the water in your tank – just the number – in degrees Celsius or Fahrenheit .

In B5 you just type the percentage of water to be changed. Just type the number (e.g. 30, NOT 30%).

In B6 you type the temperature of the tap water (let it run for a few moments before taking a reading) – again, just the number. Use the same units as in B4.

Click on the cell  B8 and in the insert line (over the spreadsheet, under the navigation banner) type the following (exactly as you see it, do not add anything; please take care to insert the right number of parentheses).

=((100-B5)*B4+B5*B6)/100

Save the file on your hard disk for future use.

In the following table you can see what the final temperature of your water will be AFTER the water change before you even start (I used normal values for my big tank). If you feel that the resulting temperature is very low (more than 3 degrees lower than the temperature of the water already in your tank) you should reduce the percentage of water to be changed until your final temperature is within the safety range.

final temperature of your tank water

input

 

 

 

 

How many liters of water are there in your tank ?

1100

Lts / Gals

What is the water temperature in your tank ?

25,8

oC / oF

What is the percentage of water you are going to change ?

35

%

What is the temperature of the tap water you have (number only)?

18

oC / oF

 

 

 

The final temperature of your water will be

23,07

oC/oF

Note: All volumes are in liters and all temperatures are expressed in oCelsius

For those of you with really big tanks, the same file can serve another purpose: it will show you how much water you changed, if you have a sensitive thermometer in your tank.

You can note the temperature of your water before the change (input this value in B5) then start the water change, stop it anytime you want (as long as you are within the pre-set temperature limit of -3oC from the initial temperature), measure the temperature of the tap water and import the values in the relevant cells. All you have to do then is to try different percentages in B5, till the final temperature shown in B8 matches the indication of your thermometer. This will be the percentage of water actually changed during the process.

This is especially useful for people (like me) who add and remove water at the same time (from different sites of course). All I have to watch is the temperature readout, stop the water change when the temperature reaches 23oC (I keep all my tanks at 26oC) and then make my calculations (to add the correct amount of my salt mixture).

You can also use the same file if you want to increase the temperature (due to a power blackout for instance). If you have access to boiled water (using gas or a fireplace for example) then the table would look as follows:

final temperature of your tank water

input

 

 

 

 

How many liters of water are there in your tank ?

1100

Lts / Gals

What is the water temperature in your tank ?

23

oC / oF

What is the percentage of water you are going to change ?

3

%

What is the temperature of the tap water you have (number only)?

100

oC / oF

 

 

 

The final temperature of your water will be

25,31

oC/oF

Which means that if your water temperature has dropped to 23oC all you need to do is to change 3% of the total volume (33 liters) with boiling water to bring it up to 25.3oC. In this example, you insert the volume of water in your tank, its temperature and the temperature of boiling water (100oC) in the “tap water” temperature. Then you insert increasing numbers in the  “percentage” cell until you get the desired temperature in the “final temperature” cell. Very simple – and it works !!

I hope I managed to give you an idea on how this can work for you. If not, you can always send me an e-mail for further information. I could then send you the excel file by e-mail along with the explanation. If someone else uses this idea to come up with a better formula, please send it to us. We will be happy to upload the file for our users. In the meantime, Happy cichliding !

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