Using high-quality water is the key to having a beautiful, healthy aquarium.
Your fish, corals and other invertebrates, as well as live aquatic plants, thrive only if the aquarium water is suitable for their particular requirements.
Tap water is rarely ideal for freshwater and marine aquariums. Your water may have too many minerals for most tropical fish. It could also contain algae-promoting nutrients.
Water treatment plants add chemicals that make the water safe to drink but unsuitable for aquarium use. Experience shows that fish, plants, and corals live longer and look better when purified water is used in the aquarium.
Fortunately obtaining purified water for your aquarium is easy. A reverse osmosis deionization (RO/DI) filtration system will provide you with clean, clear water that is free of contamination.
This guide will help you select a good RO/DI unit that meets the needs of your type of aquarium.
Tips for selecting an RO/DI filtration system for your aquarium
- One of the most important things to understand about reverse osmosis filters is that they produce small amounts of water every hour. The filtration process will produce 50 to 100 gallons per day depending on the system you select.
- You can improve RO performance by adding an optional water pressure booster pump. An RO booster pump is a small low-voltage pump that maintains the optimal pressure for the reverse osmosis filtration process. If your water pressure is less than 50 psi, consider installing an RO booster pump to ensure you get the best performance out of your filter system.
- Some RO/DI systems come with a water storage tank that collects the purified water. You can select an RO/DI filter system with a lower output if you have a storage tank since it will automatically store excess water. Many aquarists simply collect the filtered water in plastic buckets. This can be risky if you forget to check on the bucket and it overflows. The storage tank eliminates the chances of overflow and you don’t have to wait around for the water to be made.
- The individual filter cartridges will need to be replaced periodically to maintain water purity. One of the best ways to check the performance of your RO/DI filter system is with a hand-held Total Dissolved Solids (TDS) meter. The TDS meter measures the overall level of dissolved minerals in the RO water. Your RO/DI system should be producing water with a TDS range of 0-20 parts per million as tested with a TDS meter. When the TDS level starts to creep up above 50 ppm, it is time to change the RO membrane and DI resin.
Top 5 RO/DI filtration systems for aquariums
This 6-stage RO-DI systems has many features reef aquarists are looking for.
Like other RO units the water first passes through a sediment filter.
The water then flows through a granular activated carbon filter then a solid block carbon filter to eliminate chlorine, chloramines and organic compounds.
Here’s where the LiquaGen stands apart from the rest. The RO membrane housing uses a special pressure booster to force more water through the membrane and produce more water. The booster requires no electricity to operate.
The water then passes through two mixed-bed deionization cartridges, which ensure your reef tank will be safe from all traces of copper, lead, silicates and nitrate. The DI filter has an integrated TDS meter to monitor resin condition. The RO filter has a pressure gauge for at a glance system information.
- Designed to make ultra-pure reef water.
- Comes with pressure and TDS monitors.
- Makes up to 150 GPD under ideal conditions.
- Deionization cartridges guarantee safe water for your reef tank.
- Comes with a garden hose adapter for easy hook-up.
- Includes a patented pressure-booster.
- Does not include a storage tank.
The APEC Water Systems Ultimate RO- Hi-system uses 3/8” connections and tubing to deliver more water through the system.
The RO can produce up to 90 gallons of reef-safe water per day. The Ultimate RO-Hi system uses five stages of filtration.
The polypropylene sediment filter removes rust particles that can clog the filter and damage the RO membrane. Two compressed block activated carbon filters remove chlorine, chloramine and organic chemicals.
The US-made RO membrane removes heavy metals, nitrates, phosphates and other pollutants that can harm reef aquariums.
The final filtration stage captures any trace of organic chemicals with a coconut shell activated carbon cartridge. The kit comes with a water storage tank and a lead-free faucet to dispense the purified water.
- The larger tubing allows you to fill a bucket with water faster than other ROs.
- Makes water changes and top-offs for your reef tank go faster.
- Dual activated carbon cartridges to remove pesticides, chlorine and chloramine.
- High-quality RO membrane removes up to 99% of salts, pollutants, nitrate and phosphate.
- Replacement filters are readily available.
- Lifetime product support.
- Does not have a deionization cartridge.
- No flush valve to purge the system.
- No pressure gauge to monitor maintenance requirements.
The Barracuda RO/DI system uses four stages of filtration in a compact configuration that stores easily under a sink cabinet.
The rust-resistant metal frame provides a sturdy mounting system for attachment to a wall.
The blue-tinted filter housings might make it difficult to see the deionizing resin change color.
The AquaFX Barracuda RO/DI filtration system is available with a 50 gallon per day flow rate or a high-capacity 100 gallon per day model.
Consider a Watts Premier Water Filtration Booster Pump Kit if your water pressure is below 50 psi.
- Comes with a 1-micron prefilter that removes membrane-clogging iron particles and sand grains. This protects the rest of the filtration system.
- Chlorine-removing activated carbon block cartridge is rated for over 3700 gallons before replacement is required.
- Uses a high-quality USA-made thin film composite (TFC) reverse osmosis membrane for long life and consistent performance.
- The mixed bed deionization cartridge comes with color-changing resins that indicate when the resin needs to be replaced.
- The filter system includes a water pressure gauge that indicates when the RO/DI system needs service.
- The hose kit is adequate but if you need a longer hose to reach the water supply and drain, you’ll have to buy longer hose or splice the sections together.
- Works best when your water pressure is above 50 psi. If you have a well you may need a booster pump to attain 50 or 100 gallons per day output.
- The manual in the box mentions more about the rest of the product line and not much about the operation of the filtration system
The RO Buddie is an economical four stage starter RO/DI filtration system for freshwater or marine aquariums.
It is a compact design that can be mounted in tight locations. It is ideal as a temporary RO/DI filtration system that can be quickly set-up and stored away when not in use.
Many aquarists with smaller aquariums use a portable system like the RO Buddie.
The filter can be placed in the sink or in the shower when filling up a bucket of water.
The RO Buddie provides sediment filtration, chlorine/chloramine removal, eliminates minerals, nutrients, and heavy metals.
- A complete RO/DI system in a compact configuration.
- Quick and easy set-up.
- Color changing deionization resin cartridge is made of clear plastic for easy viewing.
- Quick disconnect fittings make changing the filtration components easy.
- Makes 50 gallons per day
- Does not come with hose to connect the faucet to the filtration system and wastewater drain line.
- Mounting bracket is snap-fit to the filter components and can sag slightly under the weight of water.
- Tight radius of the tubing may pose a potential leak hazard if not carefully handled.
- Instruction manual contains minimal tips and instructions.
This RO/DI system provides six stages of purification.
A replaceable polypropylene sediment filter protects the RO membrane by removing fine filter-clogging particles of grit, rust and mineral carbonates.
Two activated carbon cartridges eliminate chlorine, chloramine, pesticides, radon and volatile organic compounds (VOCs) like gasoline.
The US-made General Electric RO membrane removes heavy metals, mineral salts, arsenic, and lead.
Twin color-changing mixed-bed deionization cartridges scavenge out any traces of nitrate, phosphate, ammonia, and metals.
- Produces 100 gallons per day even at lower water pressure.
- Twin activated carbon cartridges ensure complete removal of chlorine and chloramine.
- The DI resin canisters are clear and easy to see through.
- Twin DI cartridges ensure the filtered water is ultra-pure at all times.
- Comes with a flush kit to remove carbon fines and prevent RO membrane clogging.
- Pre-assembled, just connect and go!
- 100 gallons per day may not be enough water for some aquarists.
- Does not come with a storage tank.
- No pressure gauge to monitor maintenance requirements.
What is in my tap water?
There are several sources of tap water. Your home may have a well. Other water sources include lakes, rivers, and reservoirs. Larger cities rely on centralized water treatment plants to process and distribute water to cities.
Geology has a major influence on what is in your water. When the rocks surrounding the water source are high in calcium and magnesium carbonate, these minerals will dissolve and create “hard” water. Hard, alkaline water has a high pH and leaves white mineral deposits on plumbing fixtures.
At the other extreme, some water supplies are naturally low in minerals.
This can cause copper to leach from the pipes and get into the tap water. Lead can dissolve from solder that was used to join pipes in older homes.
Disinfectants, like chlorine and chloramine, are added to kill bacteria, viruses, and other microbes. These chemicals can kill aquatic life if they are added to the aquarium! To prevent corrosion, phosphate-containing corrosion inhibitors are often added to water to protect the pipes.
Tap water contains nitrate. Nitrate enters the water supply from fertilizers, animal farms, and septic systems. These nutrients stimulate algae growth.
All of these elements and chemicals are measured as Total Dissolved Solids or TDS. TDS does not differentiate between natural minerals or harmful substances. TDS is simply a measure of all substances dissolved in water.
RO/DI systems are designed to eliminate TDS, producing water with very low TDS level.
An helpful explanation can be found here.
Why unfiltered tap water causes trouble in the aquarium?
The goal of every aquarist is to maintain the best possible water quality and do it consistently. A stable aquatic environment is essential for a thriving aquarium. If your tap water contains an extreme level of minerals, pH, and nutrients, it will be difficult or impossible to maintain stable water conditions.
Let’s take a look at a few common examples where unfiltered tap water makes aquarium keeping a struggle.
Unfortunately, many tap water sources are high in minerals and have a high ph.
Most aquatic plants cannot survive in unfiltered tap water. Amazonian fish will live but never fully develop their vibrant natural coloration in hard alkaline water.
An RO/DI system solves hard water problems by creating mineral-free water, which can be blended with a small amount of tap water to achieve the proper level of water hardness.
Adjusting and stabilizing the pH will be much easier when you use purified water in the aquarium. Spawning is often triggered by making a partial water change with purified water.
Saltwater fish aquariums
Marine fish are beautiful, have interesting personalities and can live for many years in an aquarium. Stressful conditions, however, will harm the fish and shorten their lifespan.
Marine fish are very sensitive to heavy metal contamination.
Copper, for example, is toxic to saltwater fish. Tap water often contains copper that leaches into the water from copper pipes. If saltwater fish are chronically exposed to heavy metals they become weak and susceptible to a variety of illnesses.
Chronic exposure to metals causes damage to the liver and other organs, reducing the health of your saltwater fish. If your tap water contains copper or other metals, every time you add water you are adding heavy metals!
A good RO/DI filtration system will remove all traces of toxic heavy metals from your tap water. Marine salt will also dissolve faster and leave less residue when mixed in RO/DI water.
Reef aquarists focus on raising hard and soft corals. Tropical reef corals demand the utmost in water quality. If poor quality tap water is used to make synthetic seawater the corals and other marine life simply will not thrive.
Tap water can contain harmful levels of nitrate, nitrite, and heavy metals.
Every water change and top-off add the very pollutants you work so hard to eliminate! Reef aquariums require intense lighting to stimulate photosynthesis within the corals.
If tap water contains phosphate and silicate, algae growth will be stimulated. This creates unsightly growth on the aquarium glass and rock, and can even smother live corals.
All these problems are eliminated with an RO/DI system!
How does a reverse osmosis filter with deionization work?
Large RO/DI filters are used to making injectable pharmaceuticals and other high-purity products. This same reliable technology has been scaled down, making it easy for aquarists to have ultra-pure water at home.
The process begins by filtering out fine particles like rust and sand, which can clog up the RO/DI filtration system. The water then flows through an activated carbon cartridge to remove chlorine, chloramine, and organic chemicals.
Next is the reverse osmosis (RO) process. Water is forced through a special spiral-wound membrane that separates the pollutants from the clean water stream.
Nitrate, phosphate, mineral salts and even bacteria are removed and flushed away as “reject water” containing the concentrated pollutants.
Reject water is sent down the drain while the rest of the purified water is sent to the deionization (DI) cartridge. The DI resin scavenges out any trace of contamination that slipped through the RO process.
Color-changing DI resins gradually change color as they purify the water. You'll know when to change the resin when it completely changes color.
The filtered water is collected for use in mixing up saltwater, making water changes and topping off the aquarium when water evaporates.
An in-depth explanation of the RO process can be found here.
If you have a small aquarium or require a budget RO/DI system, consider the RO Buddie 4-Stage System. The filter is easy to connect to the water supply and easy to store when not in use. Replacement cartridges and membranes are available.
This RO/DI system is well-suited for smaller freshwater and reef aquariums. There are only four filter stages to maintain, making filter cartridge replacement more economical.
For larger freshwater aquariums, fish breeders and reef aquariums the LiquaGen RO systems are
The twin activated carbon cartridges (granular and solid block) are an upgrade. This system features two large deionization filters and a TDS meter to monitor resin condition and water quality.
If you’ve got a smaller reef tank and still want the highest water quality, the LiquaGen Reef and Drinking Water Filter System has most of the same features as its big brother, but without the monitoring and pressure-booster.
If you have any questions or comments, post them below!