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Aquarium Filter FAQs

What is reverse osmosis filtration?

Reverse osmosis (RO) uses water pressure to force water molecules through a very fine membrane. Purified water is “squeezed” through the “Thin Film Composite” (TFC) membrane while concentrated contaminants are left behind. Purified water is collected from the clean or “permeate” side of the membrane, and water containing the concentrated contaminants is flushed down the drain from the contaminated or “concentrate” side. The purified water is often sent to another form of filtration called deionization.

What is deionization?

Deionization (DI) is one of the most efficient processes known for removing dissolved salts, contaminants and minerals from water. The deionization process is the removal of all charged ions from the water. Deionization uses small plastic resin beads that have positive and negative charges on the surface of the beads. The beads exchange hydrogen (H+) cations and hydroxyl (OH-) anions for pollutants and like nitrate, phosphate and copper. The exchange process “trades ions” on the surface of the resin beads. In the exchange process pollutants stick to beads while H and OH is released into the water. H and OH combine to form H2O (water). Thousands of cation and anion ion exchanges take place as water passes through the resin bed. The deionization cartridges used in APEX reverse osmosis systems scavenges out any trace impurities that make it past the reverse osmosis process.

Why is reverse osmosis and deionization used together?

While reverse osmosis alone removes up to 90% (or higher) of the common salts, minerals, metals and other pollutants, some can still slip past the RO membrane. Having deionization after the reverse osmosis process ensures that the finished water is of the highest purity (99.9% removal). This is especially important to aquarists who want to limit contaminants like nitrate (NO3-), phosphate (PO43-) and toxic heavy metals like copper (Cu 2+). APEX manufactures reverse osmosis systems with and without deionization. A standard reverse osmosis system may be adequate for your water needs. For reef aquariums containing live corals we recommend a RO system with deionization.

Can I add deionization to my existing RO system?

Yes. Apex can supply you with an add-on filter cartridge housing, DI cartridge and all hardware needed to retrofit an existing RO system with deionization. Contact our Customer Service depart for details.

Why do I need RO/DI for my saltwater or reef aquarium?

Saltwater fish and reef organisms like corals and other invertebrates rely on proper water quality to survive. The freshwater you use to mix up synthetic seawater has a direct effect on the fish and invertebrates. Marine aquarium life is very sensitive to heavy metals like copper. Tap water that is considered safe to drink can still be very bad for saltwater aquarium use. Many tap water supplies contain phosphate, which is harmless to drink. But in the aquarium it causes explosive algae growth. Using RO/DI water to make saltwater and for top-off water is the only way to make sure your aquarium water is consistently safe for your fish and invertebrates.

What is a multistage reverse osmosis filter?

An advanced reverse osmosis system will have several stages of filtration. These include:
  • Sediment Stage: Removes submicron particles, sand and rust.
  • Carbon Stage: Removes chlorine and chloramine along with organic chemicals which could damage the TFC reverse osmosis membrane.
  • Reverse osmosis stage: Removes dissolved solids and virtually everything larger than the water molecule itself. This is where the bulk of the purification is accomplished.
  • Mixed bed deionization: Removes traces of salts, heavy metals and other pollutants

Can I use reverse osmosis in my freshwater aquarium?

Yes. There are several reasons to use RO water in freshwater aquariums:
  • South American river aquariums that require water with a very low mineral content
  • When growing live aquatic plants that like a low mineral water with an acidic pH
  • When breeding cichlids like angelfish, discus and neon tetras
  • Anytime when your tap water is unsuitable for keeping aquarium fish
  • When your tap water contains algae-promoting phosphate and nitrate

I don’t have a specialty freshwater aquarium. I just want to reduce the water hardness and a keep a neutral pH.

Many tap water sources are too hard and have a high carbonate level. This makes adjusting and stabilizing the pH difficult. Blending RO water with your tap water allows you to create the right hardness and carbonate level, which makes adjusting the pH easier.

Do water filter cartridges last forever?

No. APEX uses only the finest water filtration media in our filter cartridges. Filtration media are designed to capture pollutants inside the cartridge. This means that eventually the filtration media will become full of pollutants and need to be replaced.

When should I replace my filter cartridges?

Every APEX water filtration product has a specific maintenance schedule. Take a look at the product manual, the APEX website or ask one of our customer service professionals for assistance.

What will happen if I don’t change my filter cartridge?

If the water filter is not serviced properly it will no longer function as designed. The water quality leaving the filter will no longer be purified. As the filter system become clogged, flow rate will decline. Failing to properly maintain the filter could cause damage to the filter and void your warranty.

I have a well. Can I have an RO system?

Yes. APEX RO/DI systems are compatible with a well water supply. If your water pressure is too low an RO system won’t function properly. APEX offers RO booster pumps that raise the incoming water pressure to correct level. An add-on booster pump automatically turns on and off as needed by the reverse osmosis system.

Is spring water the same as RO/DI? Can I use it in my aquarium?

No. Many people believe that spring water is the same as purified water. On the contrary, spring water contains most or more of the same minerals and impurities found in well and tap water. The purity of spring water is comparable to most municipal tap water sources. There is no benefit to using spring water in your aquarium. Over time an APEX RO system will pay for itself compared to buying distilled or even bulk RO water from an aquarium shop.

Can I purchase replacement filter cartridges and RO membranes direct from you?

Yes. APEX can supply replacement filter cartridges, membranes, filter parts and components.

Can I use any brand of replacement filter cartridge in my APEX system?

APEX replacement filter cartridges are guaranteed to fit your APEX filter. Other brands should not be used. APEX replacement filter cartridges are manufactured from BPA-free materials and high-quality filtration materials. Only APEX replacement cartridges are guaranteed for exact fit and proper water purification.

Do APEX water filters add silver to the water?

No. We do not use silver-impregnated activated carbon in our filters.

Can I drink the water from my APEX RO/DI system?

Yes. APEX RO/DI filtration systems use human-grade non-BPA plastics and only the highest quality filtration materials.

What will an APEX RO/DI system remove?

Reverse osmosis/deionization removes salts and most other dissolved inorganic substances present in the water. Reverse osmosis water filters are the best technology when the drinking water contains nitrates, phosphates, silicates, heavy metals or other dissolved substances that are difficult to remove by other methods. APEX filtration systems use an high-quality activated carbon filter to remove chlorine, chloramine and organic chemicals that get through the sediment pre-filter. Reverse osmosis, inconjunction with DI produces water with a purity that approaches distilled water. APEX RO/DI filtration systems will remove the following substances which are of special concern to aquarists:
  • Nitrate
  • Ammonia
  • Nitrite
  • Phosphate
  • Silicate
  • Lead
  • Copper
  • Radon
  • Pesticides
  • Chlorine and Chloramine
  • Natural Organics
  • VOCs
  • Petroleum products
  • Pharmaceuticals

I’ve heard that RO water is acidic. Won’t this harm my fish?

Pure water contains no pH stabilizing (buffering) minerals. Carbon dioxide in the air will dissolve into pure water and give it a low pH if tested with a pH meter. Even though the pH is acidic it does not mean the water has strong acid properties. It is not corrosive because it is only very slightly acidic due to the natural carbon dioxide gas dissolved into the water.

I read that pure water has a neutral pH. Is this correct?

Yes and no. On paper and in theoretical terms pure H2O will have a neutral pH. But that is not the real world. The very second pure water is exposed to air, carbon dioxide will dissolve into the water, slightly acidifying the water. If a few drops of tap water with a pH of 9.0 are added to a gallon of pure water, it will have a pH of 9.0. Distilled and RO/DI water will take on the pH of whatever is added to it.

Will RO water make the pH in my saltwater aquarium unstable?

No. The marine salt mix is formulated with the correct pH buffers. This ensures the pH will end up between 8.2-8.4. The pH buffer sets and holds the pH, not the RO water. All aquarium pH buffers actually work best in purified water.

I’ve heard that RO water is acidic. Won’t this harm my fish?

Pure water contains no pH stabilizing (buffering) minerals. Carbon dioxide in the air will dissolve into pure water and give it a low pH if tested with a pH meter. Even though the pH is acidic it does not mean the water has strong acid properties. It is not corrosive because it is only very slightly acidic due to the natural carbon dioxide gas dissolved into the water.