Makeup Water Systems
What your tap water has in it will determine what type of filtering and treatment it needs before being used for fish. For instance:
What type of disinfectants are used: chlorine, chloramine, other?
Did any micro-organisms survive the disinfectant? (Cysts are hard to kill!)
Are undesired metal ions in the water: copper, iron, zinc, other?
Is the water turbid or clear?
Is the water ph far from neutral 7.0: acidic or basic?
A typical high quality water system for a mid-sized application (1000 gallons) might includes the following:
Particle filter - Removes particles that could damage the R/O membrane.
Charcoal filter - Removes chlorine, chloramine, TCE, PCE, MTBE, and other trace level organics.
R/O (Reverse Osmosis) filter - Removes most of the salts (99%), dissolved inorganics, and microscopic organisms (parasites and cysts).
Optional - DI (de-ionizer) - Uses a mix of cation (removes calcium, magnesium, sodium, iron, and many other dissolved metals) and anion (removes chlorides, carbonates, phosphates, nitrates, and more) resins to remove any dissolved ions.
How much water storage is required depends upon the number of gallons in the fish tanks, plumbing, and circulating system. For a 1000 gallon system with a 10% daily change out, a 100 gallon tank works well.
The rate of R/O water filtering is more important than the quantity of water stored. In general, the R/O filter should be able to supply 25-100% of the system daily water requirements. This would be a minimum rate of 250 gallons per day, which would require 4 days to completely drain and refill the system. A 600 gallon / day R/O unit would supply twice the volume at only 15% more cost and cut the refill time in half.
Salts and buffering agents need to be added to the water to maintain a conductivity reading of 200-400 micro-siemens. This can be accomplished using a conductivity meter / controller, a metering pump and a concentrated brine solution. Alkalinity can be enhanced by adding some aragonite to the final bag filter in the sump area, rather than adding a ph controller / calcium generator to the makeup area.
Water Makeup Unit Operation (see drawing)
A solenoid valve controls the flow of tap or well water to the pre-treatment / R/O filter group. When the water level in the prepared water tank goes below the limit switch, it turns on the solenoid valve, causing water to flow into the pre-treatment module. There a 5 micron particle filter removes any sediment that could damage the R/O membrane filter, and two charcoal filters in series remove any chlorine / halides in the water, which could also damage the R/O membrane. Finally the water flows through the R/O membrane, and into the prepared water tank. A constant stream of water flushes molecules too large to pass through the R/O membrane into the drain, keeping the membrane from blocking. As the water tank fills, the upper level switch turns off the solenoid valve and the water flow stops. The tank is kept between 70% and 100%.
Water is circulated through a loop that mixes the R/O water with the salted water. A conductivity sensor reads the salinity of the solution as it passes, and when low, the controller turns on a metering pump that adds salt brine into the loop. As the conductivity increases to the set point, the controller turns off the metering pump. The prepared (salted) water also flows out of this loop to the racks as part of the water change out or for tank filling.
Water Change Out - Thoren Aquatics uses the same type of water valve for water change out as is used on the rack to supply each 3 liter tank. For a 5% change out on a 1000 gal. system, 50 gallon over a 24 hour period would flow through the valve into the sump, causing 50 gallons of water to overflow the sump and end up in the drain. This is a flow rate of about 2.1 gal./hr. (about ½ turn on the valve). For a 10% exchange, flow rate would be about 4.2 gal/hr, about 1 turn on the water valve.
Note: Conductivity checks on the water system sump should be done periodically. If there is a high evaporation loss, it may tend to concentrate the salts, resulting in higher than desired conductivity. It may be necessary to add some R/O water directly to the sump periodically to bring it back to the desired level.
Water pressure between 35 and 80 PSI is required for proper R/O operation. If the pressure is too low (high rise building > 10 th floor), a booster pump may be added... if the pressure is too high , a pressure regulator can be added.
Some facilities prefer to have a second tank with R/O water on hand. In this case, it would be preferable to place the R/O tank on a rack above the prepared water tank. This allow the R/O tank to be filled directly from the R/O filter and gravity flow from this tank would maintain the water level on the prepared water tank. If it is not possible or not desired to stack the tanks, a pump could be easily added to the setup and the tanks placed side by side.
Scheduled Maintenance: The particle filter and two charcoal filters on the pretreatment section, as well as the R/O membrane need to be changed periodically. A water analysis can provide an estimate of changing intervals for the carbon filters. A change of 15 % in the pressure drop across the R/O membrane indicates that cleaning is necessary. A significant (but gradual) increase in conductivity of the R/O water indicates that it has started to pass salts and needs to be changed.