Toxins in the Water: The Invisible Culprit.
Heavy Metals such as copper, iron, zinc, and lead destroy the fish's slime coat, cause blood patches, cloudy eyes, listlessness, and damage the gills, eventually leading to death. Keep all metal out of the tank. If you have problems you cannot identify you may be able to link them to contamination from old copper pipes. While copper is sometimes used to cure protozoal diseases, the concentration used for this purpose is relatively safe. When treating fish with copper make sure your water conditioner does not deactivate heavy metals or it will have no effect.
Symptoms: Low-level, chronic cases: Loss of colour, or darkening or "off-colour": loss of appetite; prone to fin rot, fungus, or other infectious diseases. Loss of interest in breeding.
In acute cases:
Peculiar swimming, rapid gill movements, darting after a
long period of inactivity, gasping, cloudy or protruding
eyes. All fish in the tank would be affected. Fish will
often jump out of a toxic environment.
Other Toxins include chlorine, chloramines (easily removed with a water conditioner), chemical sprays used in the home, tobacco (via fumes or from fingernails put in the water), paint fumes, and unsuitable plastic decorations (do not use if it smells strongly of plastic). Some plastics can release phenols or other chemicals into the water that are poisonous to fish. These include polypropylene and materials containing plasticizers, which are slowly dissolved in the water. The plastic turns slippery, then dry and brittle. Check any items not made for aquariums by inserting them in hot water for several hours. If there is still a plastic odour, do not use them.
Dead snails will quickly pollute an aquarium and kill the fish.
As well, watch out for galvanized buckets and water from recently decalcified water heaters.
Types of Water
Tap water is generally the safest water for guppies. Chlorine will evaporate when water is allowed to sit overnight, but if your water supplier adds chloramines, this must be removed with a water conditioner available at your local fish store ("lfs"). When you change water and notice that the ammonia level rises, this may be due to ammonia being present in your tap water, as water supply companies may add it to make the chloramines more stable. Some water conditioners will remove it. Get familiar with your water supply by running simple tests from different taps, and make sure you have properly conditioned replacement water to make it similar to the water the fish are used to prior to adding it to your tanks.
Rainwater can be unsafe due to harmful chemicals being collected in the air as it falls to the ground (this is called acid rain). Rain that has run through eavestroughs and drain pipes is even more lethal. Rainwater, distilled water and de-mineralized water are too pure and lack a number of trace elements such as magnesium, potassium sulphate, and calcium which guppies need. Simply adding salt does not fix this.
Uncycled Tanks
A brand-new tank or one that has been medicated with chemicals which destroy the helpful bacteria will prove deadly to fish unless some cautionary tactics are used (see Question 10 on Guppy FAQ's page for more details and a link).
The "Cycle": a vital process...
Ammonia/ammonium (NH3/NH4) is produced from the breakdown of protein for energy and is excreted through the gills (a type of urine). NH3/NH4 is also produced by feces, decaying food, dead snails and fish, and decomposing plants. Ammonia is converted into nitrite (NO-2) by 'helpful' bacteria called Nitrosomonas. Nitrite is further oxidized by Nitrobacter bacteria into Nitrate (NO-3). This aerobic process uses oxygen (O2), and in an oxygen-starved tank (i.e. a crowded tank with debris and little aeration), the bacteria works at a slower pace, and ammonia and/or nitrate will accumulate. In fact in the absence of oxygen, an anaerobic process will take place wherein bacteria converts nitrate back to nitrite or back to ammonia/ammonium in order to regain oxygen.
When first setting up a tank one must take the time to cycle it in order to make it safe for fish, or the result will be dead pets. Most pet stores are not helpful in this area, and will gladly sell fish to people at the same time, or the next day, of buying their first tank. Even though the first fish die, the store sees you soon again as a repeat customer, since you have already invested in a tank set-up. The way to beat this "cycle" - if you will - is to use the popular, but unpublicized, "fishless cycling" method. Fish are not necessary to gain the necessary helpful bacteria; ammonia is. I suggest you search the internet for more information on fishless cycling.
If you have a tank already set up, it is fairly simple to cycle a second. I set up tank after tank with this way: In a clean tank, add at least 50% water from a well-cycled tank, a cycled filter, and other ornaments or plants from other tanks if possible. The filter may have been set up as an extra on a cycled tank for several days, or may be a filter that has been in use for some time on another tank-with the newer filter that has been running for several days left on it (seed it with used media). To such a "new" tank, I add fish and carry on my usual frequent water changes. Just maintain good aeration and do not overfeed.
Ammonia is deadly to fish and will not be converted into nitrites quickly enough in an uncycled tank. Water changes should be carried out for the safety of the fish and the ammonia levels monitored with a test kit. Ammonia levels should be below 0.1 mg/litre. Ammo-Chips and other ammonia removers, which can be added to your filter, help in removing ammonia, however, they also inhibit the natural growth of helpful bacteria to accommodate the tank's bioload; they should only be used in case of temporary overcrowding or a hospital tank set-up.
Nitrites are the result of ammonia/ammonium being oxidized by bacteria. Nitrites are lethal but less toxic than ammonia, and guppies can handle them better than other fish. Nitrites break down the red blood cells and oxidize the iron. As a result, oxygen is inhibited from being carried through the bloodstream and causes "Brown Blood Disease". Symptoms of nitrite poisoning are listlessness, anoxia (oxygen starvation), and dark spots on the liver, spleen and kidney. Hard water has reduced nitrite toxicity. Adding salt greatly reduces the toxicity of nitrite.
Nitrates, still less toxic than nitrites, must also be kept in check. Water changes are the only way to remove them, however most plants utilize nitrates and reduce them as well. Adding salt to your guppy tank will make nitrates more toxic. When nitrates climb to 100 mg/litre, a water change is in order.
If you suspect toxins of any kind, carry out a 50% water change immediately and find the source of the trouble.
Water Hardness
Water that contains a lot of calcium salts is considered "hard" and when it has little it is known as "soft." Hardness is measured in degrees (one degree is equal to 10 mg of calcium or magnesium oxide per litre of water).
GH is the total amount of dissolved minerals (basically calcium and magnesium). Permanent and temporary hardness, two different types of hardness, make up the GH.
KH (expressed in degrees, dKH) is really the buffering capacity of the water to keep a stable level of pH. It is a scale of measurement of alkalinity (or carbonate hardness). Testing for KH is reading basically the total amount of calcium carbonate and calcium bicarbonate.
pH
The pH scale identifies the acidity and alkalinity of the water on a scale of 0 to 14. A pH value of 7 is considered neutral; pH below 7 is acidic and a value above 7 is alkaline.
The pH scale is logarithmic, which means that each number is 10 times stronger than the preceding one. Therefore, a pH of 5.5 is 10 times more acidic than water at a pH of 6.5, and 100 times more acidic than 7.5! A change of .3 per day is stressful, and death in guppies is often seen when they undergo a quick change in pH. A drop in pH may be caused by an increase in carbon dioxide or fish wastes. An increase in aeration or partial water change may correct this by expelling CO2.
Items in the aquarium that will alter the pH are shells (crushed or otherwise), dolomite or sands containing lime, magnesium or calcium, marble and coral. Unless you are trying to make the water harder and more alkaline, keep these out of your tank. Sometimes water will come out of your tap at a pH different from what it is in the aquarium; in that case it should be aged until it is the same pH as the water in the tank or the tank's pH will suddenly be changed. This is usually a result of CO2 being expelled through aeration which brings the pH up. For most guppy keepers, altering the pH (whether using pH adjusters from stores or otherwise) is not recommended and may cause serious problems for the fish as pH fluctuations will eventually occur. A stable pH is important for guppies. Keep a test kit on hand to monitor the pH.
Acidosis occurs when the fish is subjected to a low (acidic) pH. Low pH itself will increase the guppy's susceptibility to disease. A rapid change will cause the fish to be excitable, swim rapidly, gasp, and jump and soon die. When the change is more subtle, slow death will occur with few symptoms.
Alkalosis is less frequent among guppies since they can withstand a high pH (up to about 9.0), however a rapid change will cause death in a way similar to Acidosis. Also, the fish's gills and fins will be destroyed. Ammonia is more toxic in higher pH values.