Most saltwater hobbyists utilize RO/DI water for their tanks. They either purchase it from their LFS, or make it themselves. You never want to use tap water because of all the chlorine, chloramines, heavy metals, and other dissolved solids. You could purchase distilled water, but that gets expensive, especially with a larger tank.
RO/DI filters are a bit complicated and expensive, but they will pay for themselves in both money and time! All RO/DI filters contain the following elements:
- Sediment Filter
- Carbon Filter
- RO Membrane
- DI Resin
So why are some bigger and more expensive than the others? Let me explain.
- RO membranes- by adding a second RO membrane, you can double your clean water output.
- DI Resin- by adding a second DI resin canister, you can clean the water even more, especially in areas with high chlorine and chloramines.
- TDS Meters– fancier models come with inline TDS meters to let you know when it’s time to change a filter.
- Booster pump- if you have low water pressure, a booster pump can be added to make your RO/DI filter more efficient.
One of the first purchases I made in the hobby was a 7-stage RO/DI filter with two RO membranes and two DI resin canisters. Best purchase I ever made and I still use it to this day!
5. AquaFX Barracuda RO/DI Filter - 100 GPD
Numbers five and four on this post are pretty much the same thing. This one you can purchase on Amazon and #4 is from Marine Depot.
This is your basic 4-stage RO/DI filter with 1x sediment block, 1x carbon block, 1x RO membrane, and 1x DI resin canister.
As long as you have strong water pressure (let’s say above 60psi), you will be able to produce about 100 gallons of clean water per day. This is plenty of water if you have a small tank.
This AquaFX Barracuda comes with a water pressure gauge, which is handy, especially if you are unsure what your current water pressure is!
4. Marine Depot KleanWater 4-Stage Economy RO/DI Filter - 100 GPD
This is the most basic RO/DI filter you can purchase. No bells and whistles, no inline TDS meters, and just a single sediment, carbon, RO membrane, and DI resin container.
I now live in Southern California, and this would not be the best option because I would have to be constantly replacing the filters!
But, if you want to save some money and your water source is good, then why not go with this KleanWater 4-Stage RO/DI Filter?!?!
3. Marine Depot KleanWater 4-Stage Advanced RO/DI Filter - 100 GPD
This is almost the exact same as option #4. It has the exact same filtration capacity, the exact same number of stages, and the exact same clean water output.
So why is this one $50 more? Because it includes an inline TDS meter as well as a pressure gauge.
I used to have low water pressure in my apartment, somewhere around 35 psi. I could run this filter all day and not get 100 gallons. But now my pressure is at 75 psi, and the RO membrane is much more efficient!
The inline TDS meter is handy, but you really need to have a couple of these. While it is nice to know what the TDS of your tap water is, you also want to know what the TDS is after the RO membrane, and what the TDS of the final product is. That way you will know when it is time to replace your cartridges.
2. SpectraPure MaxCap 5-Stage RO/DI System w/Manual Flush - 90 GPD
This MaxCap unit is quite a bit more, but has some serious upgrades from the previous RO/DI Filters.
It also comes with a manual flush valve for the RO membrane. It is best practice to flush out your RO membrane before and after using any RO/DI filter, as it will prolong the life of your RO membrane and flush out the dissolved solids.
Lastly, this unit not only comes with a pressure gauge, but also two inline TDS meters. The first one is after the RO membrane, and the second one measures the clean water output. This is still a 90 GPD unit, but you could always purchase an upgrade kit and add a second RO membrane to double that.
1. SpectraPure RO/DI Filter With Manual Flush - 180 GPD
This unit would be my personal choice if I was a beginner. It is not the most expensive, but with the addition of a second RO membrane, the output doubles.
This is a five-stage RO/DI unit, with a pressure gauge, inline TDS meter, and RO manual flush valve.
I would also buy a separate, handheld tds meter to monitor the output, as this inline TDS meter is measuring the output after the RO membrane.