What is RO, and is it the same as a water softener?

Reverse osmosis is the process of pulling out all charged ions in water. Which is the stuff that you want out. In fish keeping RO tends to be the final stage in a number of stages. Most of us use 4 or 5 stages, but I’ve seen 7 stage filters a few times.

I personally use two stages of mechanical filtration to take out the larger stuff, and when I say larger that includes a lot of the bacteria found in water. Then carbon, and finally RODI.

The aim is to give me water with nothing in it. That water isn’t great for fish, so I then add back in the minerals and addatives I want. If I’m going for a low pH tank that will be acids, mostly using a home made botanical extract. If I want it for a normal pH range then I add buffers. I make my own based around limestone flour, which is the bulk of what you get in water in terms of minerals anyway. I add some other things depending on the region the fish has come from, but the base is ground down limestone.

Water softeners tend to replace the calcium and carbonates with other ions, often salt, that’s why you recharge the filters with salt water in some set ups. Whilst these ions aren’t going to show up on your test you’re still going to have the same issues.

What filter do you need?

Not sponsored by Finest Filters in any way, but this is the filter I used for about a decade, till I dropped it once too many times. But a friend was giving away an almost identical set up with the RO-Man badge on it. So I cobbled the two together. Got a few bits from Finest and now I have a 5 stage frankenfilter.

The positives about those are that they are relatively cheap, the replacement filter cartridges are cheap and easy to get hold of. They fit under your sink, or you can get this and attach a hose pipe just make sure that one fits your tap or hose pipe.