Water Quality: An In-Depth Beginners Guide to Perfecting Aquarium Water Chemistry

Water Quality: An In-Depth Beginners Guide to Perfecting Aquarium Water Chemistry

Water quality is essential for success in keeping any aquatic life, so it is vital to understand what goes into maintaining good water quality. The basics of keeping the best water quality possible will apply to any type of fish housing, whether that be a pond or a reef tank. This article will give a broad outline of the necessities of keeping great water quality.

Water Source

Having a quality water source is the foundation of attaining good water quality. Most aquarists in the United States have the option of either city water or well water.

Bacteria, heavy metals, and other impurities can make its way into well water which means that water parameters are not always stable and may require further treatment to become safe for humans let alone aquatic life. Most wells are drinking safe if well maintained, but this alone is usually not enough for keeping delicate aquatic life alive.

City water usually contains chloramine, which does not neutralize by sitting out for 24-48 hours as chlorine would. Both chlorine and chloramine are toxic to any aquatic life so it is important to neutralize them properly with a water conditioner, which in this case I recommend Seachem's Prime product which will neutralize most impurities in the water. 

Water Source Purifiers

Depending on your mineral content, you can usually get away with keeping most hardy aquatic life in your aquarium. Usually adding a conditioner like Seachem Prime will detoxify most impurities making it safe for life in your aquarium, but your tank will still need an additional filter with carbon to ensure it remains safe for your inhabitants. 

Even if you do add Seachem prime, this does not address the mineral content level. If you have hard water and are looking to keep a saltwater tank with hard water, then good luck! This will stress out your inhabitants and the extra minerals will lead to algae growth rapidly. Issues with hard water in freshwater aquariums are algae growth and the inability to keep soft water fish & plant species.


Soft water will usually come with a lot less problems for those of us looking to keep soft water species of fish and saltwater tanks. It’s possible to keep even soft corals and possibly anemones in soft water mixed with a proper salt mix! There are still a lot of risks when using soft water from the tap, especially in a reef tank, so be very careful.

Reverse Osmosis units are great at removing most of the impurities needed to keep most fish and inverts alive, but it can still leave impurities in the water such as copper, phosphates, ammonia, and more that only a deionization unit could take out. Even though a RO unit may remove most impurities leaving them close to undetectable, this is unacceptable for attaining the best water quality possible. 

I always recommend using an RODI unit from Bulk Reef Supply (I personally just upgraded to the 7 stage premium system). If you are unable to have an RODI unit, we sell RODI water and plenty of premixed waters that are good for reef tanks and freshwater shrimp/planted tanks. There is not a single store within a 50 minute radius of us that sells RODI water, which is essential for maintaining pristine conditions for most aquatic life.

An RODI unit using 1 micron sediment & carbon filters with proper resin will strip ALL impurities in your water. Be sure to use a proper salt mix or proper remineralization products to attain levels that will maintain the life you intend to keep!

Factors That Can Negatively Impact Water Quality

Assuming you choose to go with a RODI unit and properly maintain it, you'll be starting off with water that has no impurities. There are plenty of ways these impurities are added to your tank, so we will briefly look at every main factor individually.


Foods are the biggest source of phosphorus and nitrogen in our fish tank, so it is important to monitor how much we feed our fish and that we are feeding high quality foods that will not ruin our water quality if left uneaten. 

Either way, any high quality nutritious food will have some phosphate in it. Being aware of the phosphate contents for the food we are providing our fish and not overfeeding can be huge benefits and assist us in avoiding unsightly algae.

I like to feed my fish with the flow on unless I am spot feeding seahorses, corals, or other critters that need target feeding. Doing so, I slowly feed over a period of 2-3 minutes when my fish are usually full and stop taking anymore food. Tossing in all the food at once leads to a lot sinking to the bottom, which is fine if you have a good clean up crew or waste removal methods, but it's still it's best practice to make sure as much food is consumed by our fish as possible. 

Organic Impurities:

Other than food breaking down, there are other impurities that naturally occur in our reef tanks. Anything that consumes food rather than photosynthesizes will produce biological waste in our aquariums. Fish urination and respiration both release ammonia directly into our tanks. Fish poop and other decaying organic materials such as dead invertebrates or coral ejaculation will also break down releasing toxins into our water.

Anthropogenic Impurities

Oils that come off our hands, dust from our rooms, chemicals from our air fresheners, and many other daily impurities created by us are known anthropogenic impurities. These everyday household impurities will always make their way into our aquariums. The true extent of these toxins reaching our water is not known, so it is very important to proceed with caution.

A strong biological filtration will assist us in breaking down toxins that are released from anthropogenic impurities that travel throughout our rooms all fall in our topless reef tanks. Chemipure or even regular old carbon will solve this issue for us though.

How to Maintain Pristine Water Parameters

In reef tanks, a clean-up crew is essential for removing any food that is uneaten by our fish or corals. Finding good cleaners such as sand sifting stars, tiger tail cucumbers, fighting conch's, and other detritus eaters will assist us with the reduction of water quality deteriorating due to impurities building up. 

Protein skimmers also assist us in removing waste in our tanks by pulling out organic compounds which break down and cause nitrate, phosphates, and other impurities that can harm our fish and corals or promote growth. These are more trouble than they’re worth if you’re not using them for large commercial purposes, so we do not waste our time with this, but lots of reefers find this as a vital tool.

Having a good filtration chamber (whether it be sump, HOB, or even canister) will also yield great results. Using filter floss to trap particles of all sizes is a great first step, but we can always improve by adding chemical filtration and natural macro algae to filter other impurities in the water. 

Saltwater systems can add a refugium, usually added via a sump, which allows macroalgae to grow. Macroalgae is a great way to export excess nutrients in our tanks, as they feed off of phosphates, nitrates, etc, and keep their levels in our system very low.

Corals are not plants, contrary to the belief of some. They are classified as animals, and their bioload is sometimes equal to, but usually greater than their intake of nutrients from the water. In an established full reef tank, a net neutral bioload may be met meaning your coral colonies are actually up taking enough impurities where you can get away with no water changes if you’re dosing proper nutrients that your corals will uptake. 

In freshwater systems, shrimp such as amano shrimp are great for eating algae and leftover food particles in the tank. Nerite snails are a good invert for eating detritus and film algae on the glass of the tank. Plants do a great job of absorbing excess nutrients to keep our water less contaminated. 

Regardless of chemical filtration, natural filtration, and organisms that assist us in keeping our tanks clean; water changes will most likely be needed to keep our tanks crystal clear. There will eventually be a build up of particles somewhere whether it be under our rock work, in our sump, in a dead-zone, or anywhere else. Water changes will be sometimes the only method that will be able to remove untouched particles in our tanks.

If we have a small bio load relative to our tank size, have a heavily planted tank, or have an established reef tank, then we may be able to get away with water changes once every 3 months in these types of systems. We will still need to dose nutrients though to make sure plants, corals, and inverts are all able to thrive. 


In both freshwater and saltwater systems, filtration is the best method of prolonging our water quality and avoiding those pesky water changes every week. As talked about before, there are chemical filtration media such as purigen, chemiclean, phosguard, and others that improve our filtration tenfold.

Organic filtration is very important as well, as beneficial bacteria are constantly cycling to break down impurities in the tank to make our water parameters safe for tank inhabitants. It is important to not disrupt our substrate, rock work, or filtration media too much, as these are hot spots for our beneficial bacteria to grow. Having a large surface area of rockwork helps as well, allowing more bacteria to grow. Even plants in freshwater and macro algae in saltwater have their benefits in removing impurities.

With all these methods, most tanks still require water changes to avoid algae growth and impurities from becoming out of hand. Unless you add elements through dosing, your freshwater inverts, saltwater inverts, and corals will all need water changes to supplement those elements that they use up. 

Water changes essentially remove impurities such as excess nutrients, metals, organic compounds, and more. Ensuring we have a proper water source and are using the right additives will ensure that we are replenishing nutrients that are used up or removed during a water change. 

Proper feeding, a moderate light schedule, particle control (filter floss and protein skimmer), chemical filtration, a strong biological filtration, and other tips mentioned in this article will ensure you to be a successful aquarist. 

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