Water DI, RO, RODI

Since very few of us have natural seawater available to do unlimited water changes with, we are forced to create our own synthetic seawater.

The salt mix components can be easily adjusted with 2 goals in mind. First is to simulate natural seawater and second, to adjust the components for a closed biosystem. Our preferred salt is Crystal Sea Salt from Marine Enterprises International in Maryland. Read Julian Sprung’s review for one reason. Another reason is it’s the only salt we’ve found that doesn’t require additional builders, buffers, major and minor elements. Only monthly water changes are necessary. See maintenance

Regardless of our salt mix and unless the water used is absolutely pure, you will defeat the idea of “clean seawater”. Our standard for water purity is Total Dissolved Solids equals zero, aka TDS=0. To measure TDS you use a meter that measures conductivity.

Minerals that dissolve in water have plus (+) and minus (-) charges. For example, salt or sodium chloride (NaCl) as a solid in your salt shaker, doesn’t conduct electricity. But when sodium chloride is dissolved in water, sodium ions (Na+1) and chloride ions (Cl-1) are formed. These ions allow electricity to flow. A TDS meter works by testing how much electricity goes through your water sample. If you have pure water – you don’t have any ions. Zero ions means zero electricity can flow and your TDS meter reads 000. Dissolved ions are 1 of 3 things that are possible.

Organics are minimal in drinking water and easily removed with a carbon filter. Carbon also has the capability to eliminate other things such as chlorine.

Sediment and other particles need to be removed with a micron filter. The micron size depends on the method of purification used.

Direct De-Ionization aka DI
Purifying water by de-ionization only depends on the TDS of your local water. Portland, Oregon hasrain water and snow melt reservoir. Our TDS is under 20 which let us skip reverse osmosis –aka RO.Seahorse uses a 6 stage system.
Stage 1: 10” 20 micron string wound cartridge
Stage 2, 3: 10” cartridges filled with coconut carbon
Stage 4, 5, 6: 4” x 20: cartridges filled with a very high quality de-ionization resin.

Resins are synthetic polymers. Some have positive charges (Cation) and some negative charges (Anion). They work like magnets where positive resins capture negative ions, etc.

We can produce 1300 gallons of TDS=0 water in less than 24 hours. If your local water is about 40 TDS you directly de-ionize your water. Cold water flowing slowly is best for de-ionization.

Reverse Osmosis – aka RO
Osmosis is the process of water passing water through a cell membrane. Reverse osmosis is what it suggests. Water is passed by a RO cartridge rated in gallons per day. The gallons per day are seldom achieved so use at least a 100 gpd unit. What they don’t tell you is a 150 gpd cartridge will fit in any size cartridge case. RO works best with room temperature or warmer water. Increasing pressure inside the RO cartridge increases output. A major problem with RO is waste water. There are 5 or more gallons of waste water per gallon of RO water. Using a flow restrictor rated to match your cartridge seriously reduces waste and increases back pressure and output. Unfortunately RO produces 92 to 96% purity.

RODI Water
RO units requires one additional cartridge unit on the output hose to get TDS=0 water. Since the water is close to pure the DI resin will last a long time. It’s best to have a dual TDS meter to monitor your incoming water as well. Should you suspect your TDS meter has a problem switch probes. The length of time your cartridges last depends on the TDS of your tap water. If TDS > 150 have replacement cartridges on hand.

When your DI resins have expired your TDS meter no longer reads 000. We suggest cartridge changes when the meter reads 001. The first sign the RODI system needs its cartridges changed, regardless of a TDS meter, is the appearance of reddish brown algae on the glass.

Change your RO cartridge to 150 gpd, a 1 micron prefilter, a 5 micron carbon and new DI resin at least once a year or your TDS goes above 0 or it’s been a year, whichever comes first.

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