Ultimate guide to best reverse osmosis system for aquarium

Having spend so much time studying reverse osmosis systems, I realise by now that RO water can not only be for safe drinking but can also be used as filtered water for aquariums. In this guide, I shall go through in detail the different reverse osmosis systems that are the best for the money. No details shall be sparred so prepare some coffee and get ready for a long read! (you have been warned!)


Reverse osmosis system for fresh water and saltwater aquarium

Aquarium Ro system is very straight forward to review since they are similar to the home reverse osmosis systems that I owned and have reviewed. The only difference is the DI filter that is used to remove ions from the water. If you are this filter away, you can actually use the same RO machine for drinking water.

aquafx reverse osmosis system for aquarium reviewIn this regard, I recommend the Aquafx’s RO/DI system as the best value for marine aquarium reverse osmosis system. It not only has an attractive price point but has plenty of solid features that makes this an outstanding choice:

  • Strong purification: The best test for any filtered water to use a TDS meter and see how low is the ppm readings. In this aspect, the aquafx unit performs very well as it usually produces zero PPM reading, i.e. there are no impurities in the water at all!
  • Fast outflow: many reverse osmosis aquarium filter system has a relatively slow outflow. In contrast, the Aquafx can do 1 gal of reverse osmosis water in about 6 min and 45 seconds. That is relatively fast when compared to the portable or countertop versions.
  • Clear setup Instructions: The instruction manual that comes with the unit spells out clearly how you should hook this machine up. If you need more help, there are also youtube videos that shows up a step by step tutorial on how to do this properly. Compared to the under sink ro systems, this is much easier.
  • Solid customer service: if you have trouble in your installation or need parts replacement, the company will respond almost within 24 hours. The employees are friendly and knowledgeable so any issues can be handled effectively.

Some minor shortcomings

  • Hose is a bit short so if your tap location is too far away, you will need to buy a longer hose separately
  • High water wastage ratio: This unit needs about 4 galleons of water to produce 1 galleon of pure water. It is not unusually high but something that should be highlighted. If you want zero waste, read up on my reviews on the best zero waste reverse osmosis system.


Best portable reverse osmosis system for aquarium

best portable reverse osmosis system for aquariumComing from the folks at Reverse Osmosis Revolution, this is an affordable but high quality portable Ro aquarium system. The benefit of having a portable unit, rather than a larger one, is that it is easy to install as well as being able to move it for different usage if needed, not to mention it has a lower price point.

  • Easy to install as expected for a portable reverse osmosis system
  • Strong purification: The water, after purifying, yields a big fat zero on the TDS meter.
  • Affordable pricing as it retails about USD100

Minor shortcomings

  • Instruction manual is not clear and is obviously written by someone who is not a native English speaker
  • Water flow is not as strong but this is to be expected for a portable reverse osmosis aquarium system.


Cheap reverse osmosis for aquarium

Cheap reverse osmosis for aquariumFor those looking for the cheapest RO aquarium filter, look no further as you can’t get a price lower than this unit from purewaterclub. The catch for this low price? It works very well only on 55/64″ faucets. If you have good plumbing skills, you still can get it to work via replacement of the faucet connector. If not, I advise you to spend more money and get the aquafx model instead.

For those who have the 55/64″ faucets, then this is probably value for money RO unit you can buy. It works beautifully as any other Ro units at only a fraction of the price.

  • Cheapest reverse osmosis unit. Nuff said.
  • Quality purification as it can bring the TDS reading down to low ppm readings. The exact differs by customers. I have seen reports stating from 3 ppm to 23 ppm. Nevertheless, although it is not zero but is already very impressive given the price.

Minor shortcomings

  • Instructions are unclear, especially for the set up and the connecting
  • Fits only 55/64″ faucets, without the need for additional plumbing works
  • Customer service is spotty as they don’t take phone calls. Email communication only!


6 stage reverse osmosis system for aquarium

6th stage reverse osmosis system for aquariumFor those looking beyond the 100 galleons that the aquafx can produce, try this unit by Koolermax. It can go as high as 120 galleons which is probably the highest I have seen. Not only that, there are a bunch of cool features that make this unit worth the price it is commanding (around USD200 without discount)

  • Effective filtering: all the reviews I have read online says their TDS readings fell to zero after installing the Koolermax aquarium RO unit. That is how good and consistent the product is.
  • 6 stage filtering: all of the models mentioned above are either 4 or 5 stage RO units. This is the only 6 stage reverse osmosis system for the aquarium that is on the market. The additional stage is another DI filter to ensure the ions are truly removed.
  • Fast outflow: similar to the aquafx, this unit’s water outflow is fast and steady
  • Less water wastage: its clean to waste water ratio is around 1:3, which is lower than the 1:4 that is needed by aquafx

Minor shortcomings

Believe it or not, there is no one negative comment that came across my screen as I was doing the research. The only nitpicking I heard was its high waste water ratio but that is expected for any reverse osmosis system and Koolerman’s ratio is already low in comparison.



Depending on your setup and situation, any of the four models here is a good choice. If budget is not an issue, then the aquafx or the Koolermax will make an excellent choice as they are almost perfect. The cheapest will be from the purewaterclub. It is affordable but purification is less impressive than the rest although it can still get the job done.

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