More on Water Quality

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“I am 100% satisfied with your nitrate remover. Within a couple of weeks after setup my aquarium nitrates have dropped to virtually zero and remained there.. I’ll never be without one.” – Chris

This webpage is designed to give readers more advanced information on water quality and how to ensure optimal water quality in any aquarium using testing equipment and tap water filters. Aquaripure is dedicated to providing customers all of the tools and equipment needed to maintain optimal water quality at all times.

Tap Water Filters

Just because nitrates are low and pH is ok does not necessarily mean that the water quality is perfect for your individual tank. It is important to consider the water you use to top it off due to water lost to evaporation. If this is not taken into consideration and only tap water is used then water quality potentially can degrade over time. This fact is due to the fact that tap water in most areas is of fairly poor quality. Most tap water is alkaline (has a high pH), has high levels of calcium, magnesium, and other metals and therefore is not suitable for water top offs in many aquariums. The levels of calcium, magnesium and other metals in water is directly related to both pH and hardness. Tap water also contains chlorine, volatile organic compounds, and possibly other contaminants. Fortunately there are a number of economical solutions to ensure the water in your aquarium remains of optimal quality and balanced.

For some aquarists tap water conditioned with a carbon block tap water filter is sufficient. The water might still be slightly hard and alkaline and have high levels of calcium and magnesium. However, the carbon filter does a great job of removing chlorine, volatile organic compounds, and many other compounds not wanted in any aquarium. This water is also healthy and fantastic for humans to drink.

Reverse Osmosis filters will produce the most pure water available right from your tap. It will remove just about everything including nitrates and will produce soft water with a neutral pH. It is great for water top offs and changes in any aquarium and is great for drinking as well. To view all of Aquaripure’s Tap Water Filters click here.


First, whether an aquarium is saltwater or freshwater, is is imperative that proper pH be maintained and that the tank be adequately buffered. These are two slightly different concepts. A buffered tank will resist pH fluctuation changes which can harm an aquarium. To properly buffer a tank one should add sodium bicarbonate (baking soda) until it’s pH just begins to rise. After adding sodium bicarbonate, if the pH rises then the tank is adequately buffered. Adding more will continue to increase pH until it is at it’s proper level. Calcium Carbonate or other compounds can also be used but baking soda is the cheapest and most readily available. The buffering capacity is also known as kH but if adding baking soda increases pH then the buffering capacity is sufficient. Always add baking soda very slowly and gradually. One must avoid any sudden and drastic changed in pH.  The pH tests on test strips can be hard to read or not particularly accurate which is why Aquaripure also recommends an electronic pH meter or the API pH test kit.  If you get the kit just make sure you get the appropriate kit for high pH or lower pH tests.

What is the ideal pH for your aquarium? The best pH for a freshwater aquarium can range anywhere from 6.4 to 7.8 depending on the type of fish in your aquarium. This is why it’s so important to know your fish and make sure you obtain compatible fish for your tank. If in doubt the 7.2 pH is a good target and most freshwater fish will adapt well to this pH. For saltwater aquariums the recommended pH is 8.0-8.4 and 8.2 is an ideal target value. pH should be monitored at least once every week or two and maintained. To lower pH the best thing to do is do a water change with very soft water, either reverse osmosis or distilled water. To lower it below 7.0 one can use peat moss but this is not really necessary for the majority of freshwater tanks. A water softening pillow can also lower pH if necessary. One must monitor pH even more carefully when a pH lower than 7.0 is maintained as it will have little buffering capacity.


Monitoring pH is essential but it is a Nitrate test that will give the best indication of overall water quality once a tank is cycled. Fortunately nitrate test strips are cheap and readily available that are about as accurate as any test kit. It is widely accepted that nitrates over 40 ppm is generally harmful to fish and other aquarium animals. In many tanks and for humans 40 ppm would be considered far too high. High nitrates in a tank might be compared to humans living in an extremely polluted environment. Some healthier people might not be as noticeably effected at first but more sensitive or weaker people will more readily succumb to illness. There are many links and webpages on this website dedicated to nitrates and the effects of nitrates in a tank.

It is essential that any beginning aquarist starting a new tank be very aware of the nitrogen cycle. The is the process where a new tank becomes established with beneficial bacteria which breaks down organic molecules into nitrates. There will first be a potentially deadly ammonia and then nitrite peak before the tank becomes established. This process can last 8-12 weeks but will be greatly hastened using aquarium bacterial cultures.

Using TDS and ORP meters to monitor water quality.

Although they are not absolutely essential, the TDS and ORP meters that Aquaripure offers can give you an idea of the overall water quality in both freshwater and saltwater aquariums. In general, TDS meters are useful for monitoring the effectiveness of Reverse Osmosis units and in testing the quality of water in freshwater aquariums. ORP meters are more useful in testing the general quality of the water in saltwater aquariums.

The TDS in most municipal water supplies is quite high, often 300 ppm and even all the way up to 500 ppm or more. This is completely unacceptable for any tank as it is both very hard and contains significant amounts of unwanted compounds. It is also not even really recommended to drink. Do you really want to drink water that has more dissolved solids and compounds in it than the average lake or river?

TDS stands for Total Dissolved Solids. A TDS reading will count not only contaminants but also things you might actually want in your aquarium water such as calcium, magnesium, and other trace elements and metals. The TDS reading of most natural clean spring water will be between 100-200 ppm. Most rivers and lakes would be a little higher, possibly up to 300 ppm.

For freshwater aquariums where a more neutral or even acidic pH is desired then even a TDS reading of 100-200 ppm is too high for water top offs. Reverse Osmosis (RO) water should be used.
Reverse Osmosis (RO) water should have very low TDS and a TDS meter is very useful for monitoring the effectiveness of RO units.

The TDS in a freshwater system should range 25-75 ppm or so for Discus and other fish that require very clean and soft water. In most freshwater tanks 75-200 ppm would be considered an ideal range. For a few freshwater fish such as some species of cichlids an average TDS of up to 300 ppm would be acceptable. In nature fish might adapt to a wider range of variables but these would be considered ideal levels.

ORP, or Oxidation Reduction Potential, can also be used to give a general indication of overall water quality. ORP can be used in freshwater and saltwater aquariums. If you want a detailed analysis of the use of ORP in aquariums then you can read this article but the basic information required to use it is here. Basically if ORP is low then there are a lot of reducers in the water. Reducers include a few other compounds but are mostly composed of organic molecules. So if ORP is low then the water most likely has too much organic matter and compounds in it such as fish waste, uneaten fish food, etc.

If ORP is high then that can mean there are a lot of oxidizers in the water. The ORP is hot tubs should be at 600 mv or more. This is because chlorine is an oxidizer and a hot tub should have a lot of chlorine in it to destroy ALL organic (including living) compounds. You do NOT want your aquarium to be this high. Ozone is sometimes added to fish tanks and ORP is monitored to make sure it doesn’t go over 450. That might mean too much ozone is present. With an Aquaripure the ORP will typically rise and might even get as high as 500. This is not dangerous in this case because this is not due to oxidizers being artificially pumped into the water but rather the reducers being removed. However, you might want to add a little coral food if the ORP in a reef tank goes above 450 mv. In an aquarium an ORP value of 200-500 mv is acceptable with 300-450 mv being the recommended range.