Most people would say that when keeping a saltwater tank, it is all about learning to keep the water at ideal parameters. There are several ways you can achieve adequate water conditions for your saltwater tank, but the most popular is to use a reverse osmosis & deionization (RO/DI) unit.

If like me, you don’t have a water report to hand and your local fish store is a fair distance away, then you are probably considering getting a RO/DI unit. Personally, I found the whole topic a minefield! There are so many different opinions and options out there that it is hard to know where to turn with it.

I am not even going to attempt to talk you through how many stages you will need, there is plenty of information available on the net to help you figure that one out. But I will say what I have opted for is a less common approach.

I have opted to have an RO/DI unit that is suitable for both aquarium use and for it to produce drinking water. I chose a 5 stage domestic unit by Finerfilters, then added the 6th stage as the deionization stage.

Finerfilters Reverse Osmosis Unit
Finerfilters Reverse Osmosis Stages 1 to 5
  • Stage 1: Sediment filter to remove dirt, sand & rust.
  • Stage 2: Granular activate carbon to remove free chlorine, odor, chemicals and organic contaminants.
  • Stage 3: Carbon block filter to remove Trihalomethanes, pesticides, chemicals, giardia & Cryptosporidium cysts.
  • Stage 4: Reverse osmosis filter to remove dissolved salts, lead, copper, barium, bacterial by-products, estrogen, and silica.
  • Stage 5: Carbon filter to improve taste and removes any further contaminants.
  • Stage 6: Deionization to remove total dissolved solids (TDS)

Deionized water is not safe to drink, however, the pure water created in the 5 stages before the deionization stage has many proven health & taste benefits.

So, how does it work for both purposes? The domestic system comes with a pressurised tank to allow for a reasonable amount of water storage as these units are not the fastest at producing the water (it should also be noted that even the manufacturers state that RO/DI units can waste up to 85% of water so it may not be the most cost effective solution for everyone).

Stages 1 to 4 are stored in the pressurised tank, when the purpose fitted tap is opened, the tap then calls on water from the tank to pass through the final polishing stage (stage 5) and is then available to use as drinking water.

I have put a “T” on the pipe that goes from stage 5 to the tap which then has a small plastic tap. When the plastic tap is open, the water is then passed through a non return valve (we don’t want to drink the DI water!!) and down in to the deionization unit which will eventually be hooked up to a container to fill it with water ready to use for the tank.

RO/DI for drinking and aquarium
Full system under sink

We have tested the water with a TDS meter and after the first 5 stages it reads 0006ppm and after the 6th stage it does read 0000ppm.

What I will say is that this took alot longer than it should have done. The instructions that came with this unit were not good at all!! I have to say we found it alot easier to follow videos from another manufacturer than we did to try and follow the Finerfilters instructions.

The system is quiet & so far (1 month in) no leaks. The drinking water tastes good and so far, no ill-health from it! My partner used to complain about “fishy” tasting coffee, now he doesn’t. I would recommend this set up to anyone who makes the investment and installs one of these units. Why should the fish get all the perks, treat your families too!