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Choosing and Conditioning the Water in Your Aquarium

Choosing and Conditioning the Water in Your Aquarium

Updated February 06, 2014
Learn about how to properly choose and condition the water you use in your freshwater aquarium.
As an aquarium hobbyist, it is your responsibility to keep your fish healthy. Not only do you need to provide them with adequate space and a healthy diet, but you also have to make sure that their tank environment meets their requirements. The single most important factor in the health of your fish is the quality of your water. Therefore, it is imperative that you choose your water source correctly and condition the water in an appropriate manner. This article will help you address both of these issues.
Tap Water
The most common source of tank water for aquarium hobbyists is simply the tap – the water that runs in your home. It is the easiest source to get your water from and in most cases, works just fine. However, the parameters of tap water can vary widely from location to location. You need to test your tap water for pH, gH, kH, and nitrates to understand exactly what is coming out of your tap. If the preferences of your fish are drastically different than your tap water’s parameters, you may need to use a different water source.
Remember to always use a dechlorinator/chloramine remover on your tap water if it comes from a municipal water supply because it has likely been treated with chemicals. These chemicals are meant to make tap water safe for humans, but they can be toxic for fish. If you prefer not to treat your tank water with chemicals, leaving the tap water out for 24 hours or so may be adequate to let some of the chlorine evaporate.

Brass Water Tap by Anita Martinz via Wikimedia Commons

Spring/Bottled Water
One possible alternative to tap water is spring water. Spring water is useful if you need to lower the pH or the hardness of your aquarium’s water. The main drawbacks to spring water are its price and the fact that the mineral content varies widely from brand to brand. It is best to buy several different brands in the beginning and test each of them for pH, kH, and gH before picking the one that matches the preferences of your fish. One way to find a happy medium between your tap water and spring water is to mix the two -- this will also help cut the cost. When using bottled water, make sure it is not distilled (this means that all minerals have been removed) and that it hasn’t been treated with flavors, dyes or other additives.
Reverse Osmosis Water
Another choice is reverse osmosis water. Reverse osmosis is the process by which pressure is applied to a concentrated solution to force it through a membrane. The membrane will allow the water molecules through, but will block larger molecules such as minerals and other contaminants. There are several membrane types used for reverse osmosis:
● Cellulose Tri-Acetate (CTA) – CTA membranes are made of organic materials and produce less pure (remove 88% - 94% of impurities) water than the other two membranes. They do not get rid of chlorine from the water so you would still need to use a dechlorinator or leave your water sitting out for 24 hours.
● Thin Film Composite (TFC) – TFC membranes are made of synthetic materials and remove 94% - 98% of impurities.
● High Removal Membranes – High Removal Membranes are made of synthetic materials and remove 97.5% - 99% of impurities. These membranes are very good at removing silicates.
One problem with reverse osmosis water in freshwater aquariums is that it may be too pure -- it contains very few of the trace elements required by your fish. Therefore, it is never a good idea to use only reverse osmosis water. Instead, it should be mixed with your tap water in some proportion. You will need to experiment with different proportions to find what gives you the water parameters you need.
Another problem with reverse osmosis water is that it has zero kH and gH. This means that is has no buffering capacity and is very soft. The result can be huge swings in pH and other water parameters -- this obviously is not good for your fish. This is another reason that mixing it with tap water can be useful as the tap water will raise the kH and gH. You could instead add a commercial buffer, but you need to take caution when doing this. If you try to do 100% reverse osmosis water and add chemicals/products to adjust for the problems, you need to carefully monitor all the parameters to make sure you do not crash the aquarium.
Local Lake/River/Creek Water
While it may seem like a good idea to use water from a local source, it usually is not. It will save you money, but it may cost you in other areas. When taking water from a local source, you have no idea what kind of pollutants the water has in it or its mineral content. This can make it very hazardous to your fish. It is for this reason that local lake/river/creek water is not recommended for use in an aquarium.
Rain Water
Rain water is similar to lake/river/creek water in that you do not know what kind of pollutants are in it. The air around you may look clean, but you have no idea what the rain water picked up on its way down. Therefore, rain water should not be used in an aquarium.
Water Parameters and Problems/Solutions
● pH – pH measures whether your water is basic, acidic, or neutral. A pH of zero is the most acidic, 14 is the most basic, and 7 is neutral. Most fish prefer a pH in the range of 6.4 - 7.8, but some fish prefer a pH outside this range (for example, African cichlids prefer a pH higher than this). Despite the fish having preferences for certain pH values, most are able to easily adapt to a wide range. They cannot, however, live through large pH fluctuations (large means fluctuations of greater than 0.3 over a 24 hour period). Therefore, instead of shooting for a specific value, it is much more important to maintain a constant pH.
If you are having problems with your pH, you can read the article on this website entitled Properly Maintaining the pH in a Freshwater Aquarium. You can also try to adjust what water source you use. For example, if your pH is too high, you could try mixing in some spring water to lower it. If you are experiencing large pH swings, it may be because your kH is too low and your water does not have enough buffering capacity. You can measure your kH and then take steps to correct for low kH.

Aquarium pH Water Test by Flickr user CyberGibbons

● kH – kH measures the concentration of carbonates and bicarbonates in your water. It also indicates the buffering capacity of your water. Buffering capacity is the ability of your water to neutralize added acid without significantly changing the pH. If your kH is too low (less than 4.5 odH), you may start to have problems with large pH swings. Over time, the nitrates in your aquarium will rise and the pH will drop. Having a high buffering capacity will resist this drop and maintain a stable pH.
If you have low kH, you can add baking soda (will need to be continually added with each water change), increase the aeration in your tank (to drive out the carbon dioxide), or add chemical products (although these usual only fix things temporarily). If your kH is too high, you can add reverse osmosis or spring water to the tank, inject carbon dioxide, or use chemical products (again, this is only a temporary fix).
● gH – gH is the general hardness of the water. It is mostly a measure of the concentration of magnesium and calcium ions in your water. gH is the parameter that dictates whether you have “hard” or “soft” water. Therefore, if you read that your fish prefers soft water, they mean that your fish prefers a low gH, not a low kH. Like pH, most fish are pretty adaptable to a wide range of values despite their preferences. The biggest exception to this is during breeding for many species.
If your gH is too low, you can add rocks such as limestone to the aquarium or you can use crushed coral as your substrate (or place it in your filter in a mesh bag). These substances will also raise your pH. If your gH is too high, you can filter through peat moss, add reverse osmosis/spring water, or use a commercial water softener (although this is not generally accepted as safe for many soft-water species as it introduces sodium which many do not tolerate well).
Conditioning Your Water
Some aquarium hobbyists advocate for tailoring the exact details of your tank’s water parameters to the needs of your fish. This can be difficult in practice, however, because the tank requirements of fish may vary depending on their species and whether they have been wild-caught or commercially bred. Perhaps the better option is to condition your fish to the water parameters in your tank. The most important thing you can do is to keep your tank water clean, your water parameters stable, and to avoid adding too many substances to the water.
There are many chemical additives on the market that are designed to alter certain aspects of water quality including pH, alkalinity and more. It is difficult to find the correct dosage when using these products, however, and you can never predict the other effects it might have on your tank. For this reason, it is best to avoid using too many chemicals in your tank. The only product you should need on a regular basis is a general water purifier or conditioner designed to remove chlorine and chloramine from tank water.
After reading this article, you should have a basic knowledge of what you need to do in order to choose the right water source for your tank. As it has already been mentioned, tap water is usually your best water source as long as you treat it with a water purifier. However, some people live in places that have terrible water quality (or water parameters that do not mesh well with the preferences of their fish). If this is the case, then the addition of reverse osmosis or spring water to tap water can help. Every tank is different and the water parameters in your tank will vary depending on your water source and the type of fish you keep. The best thing you can do is to learn everything you can about what you are putting into your tank so you can make it the healthiest environment possible for your fish.

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