# Methods of Water Treatment in Aquariums

An aquarium can become contaminated with discolored water due to the waste product of ammonia that is excreted from a fish. This disrupts the pH of the water.

What is pH? Here are the facts:

The pH scale is expressed as the negative logarithm of the hydrogen ion concentration ranging from 0 (high [H+] ,acidic) to 14(high [OH-] and less

H+ ions, basic). pH is short for “pondus hydrogenii” meaning “potential hydrogen.” The pH concept was introduced by a Danish chemist, Soren Sorensen, in 1909 . The pH must be strictly regulated in an aquarium to maintain life in the tank. A good pH in the tank is between 6.8-7.2.

http://www.aquariumcareblog.com/tag/chemical-equations/

Figure $$\PageIndex{1}$$ : Aquarium ￼(aquascapingworld.com)

The pH of the aquarium water affects ammonia levels. The water can contain pure ammonia (NH3) and the ammonium ion (NH4+). Ammonia is more toxic than the ammonium ion to the fish in the tank. High pH(lower [H+]) water contains more pure ammonia, while low pH (higher [H+]) water contains the ammonium ion. Ammonia toxicity causes severe stress to fish making them more susceptible to disease and death.

The dissociation of ammonia equation is:

$\ce{NH4+ (aq) -> NH3 (aq) + H+ (aq)} \nonumber$

$\ce{H+ (aq) + OH- (aq) -> H2O (l)}\nonumber$

According to this reaction, the formation of NH3 will depend on the pH of the water. If the water contains too many hydroxide ions [OH-], the system will try to rebalance
itself by shifting towards producing more water and depleting H+.; a right shift.

This shifting is called Le Chatelier’s Principle which states:

A change in one of the variables that describe a system at equilibrium produces a shift in the position of the equilibrium that counteracts the effect of this change.

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch16/lechat.html

Restoring balance:

This system can not be shifted to the right for too long. If it is, the [H+] will become depleted. To restore this imbalance, the system now needs to shift to the left.

A green method of restoring acidity to an aquarium is by adding either vinegar, also known as acetic acid (CH3COOH) , or lemon juice which contains citric acid ( C6H8O7). When these are dissolved in water, they increase the [H+] concentration. According to Le Chatelier’s principle, the reaction would proceed to the left to compensate, lowering the toxic [NH3] and increasing [NH4+]

Chemical Methods of Water Treatment :

Chemical methods to rid the tank of ammonia are costly and involve ordering from various companies. One such product is called granular zeolitic medium that absorbs ammonia. A zeolite is a composite of over 50 different minerals in a lattice structure that contains a network of interconnected tunnels and cages. Water moves freely in and out of these pores but the zeolite framework remains rigid and acts as a molecular sieve. Some individuals use this method because they are unaware of possible negative side effects such as the zeolite becoming covered in ‘gunk’ over time and the cost accumulation over the lifetime of a tank.

http://www.tropicalfishfinder.co.uk/...s_articles.asp

Figure $$\PageIndex{2}$$ Zeolite Lattice

http://www.chemeddl.org/resources/models360/solids.php#zeolite

Videos: http://www.youtube.com/watch?v=PpIAChuW4Kw - this shows a natural aquarium with no artificial filters or chemicals.

http://www.youtube.com/watch?v=k3DqqKGO47k - this shows the chemical testing of water cheap contact lenses

From ChemPRIME: 13.0: Prelude to Equilibria