We will be installing a whole house RO in a home with copper pipe. We plan to use an inline calcite filter to neutralize the expected low pH. Should it be installed between the RO and the storage tank or after the storage tank and repressurization pump? Should it be upflow or downflow?
The pH before the RO is 7.17 and the TDS 2869 mg/l. We expect a permeate flow between 1.5 and 2.0 GPM.
It is more economical to install the calcite filter on the RO permeate line to the tank since the flow is much less and constant. A 10 or 20 inch cartridge which can be refilled is much easier for the homeowner than a FRP tank with distributor. I don't think the flow direction matters; generally the cartridge type filter is upflow. Without the filter our experience is that the customer will have staining from both the copper and the chrome plated brass fixtures. Also the 400 series SS in a dishwasher can rust without pH correction.
This can be also done by companies who make these cartridges with a mix of magnesium oxide/ calcite. Sometimes the calcite alone does not react fast enough. It has been my experience that on a whole house system like what you mention some other considerations should be looked at that are commonly missed. To name a few.... 1. Protection for system if tank runs low or supply is or gets weak. 2. Customers 9 out of 10 times do not properly take care of unit, cover yourself. 3. Storage tank if atmospheric needs cleaning and sanitizing. 4. If ozone is used, make sure to vent outside...One company who advertises heavily these systems uses ozone and did not vent it out. Customer went on vacation and ozone kept running and ruined many items in garage. 5. Sizing is important, just because a family of four may use 300-400 GPD does not mean that a 400 GPD RO system is the answer !! 6. NEVER compete on the cheap !! One liability claim can easily wipe out profits of many units with the way insurance companies are raising rates when a claim comes in. EDUCATE, JUSTIFY, SATISFY...All will win in the end.
I disagree with the cartidge to make it easy to refill. An upflow neutralizer with a dome hole can be easily refilled by a home owner and will hold a substantial amount of material thus not needing constant refilling. Since it can be sized larger it can also be placed after the repressurization pump if that is desired.
A upflow neutralizer is a good choice if you have a large system and are able to fill unit as per needs. When we put the system together, we already know we are going to be out every 3-6 months to replace other filters and checking the system over (as stated, most customers won't on their own) and make any adjustments or changes necessary. We also have opportunities with this type of set-up to change the PH if necessary where as a upflow tank is a less forgiving in making changes if needed. There are 1001 ways to put together a whole house system, many people offer many different solutions and with proper planning and servicing, many types and styles to choose from for the benefit of both customer and supplier.
Since the RO be small (1500-3000gpd normally for home) a small 9x18" tank is fine, plumbed in reverse so it has an up flow, install between storage and the RO. Mix the media 1/3rd Corsex 2/3 calcite and only with only about a 9" bed depth. Install a 3 valve bypass so you can control the amount of water feeding the tank and bypassing. Install a sample port after the tank so you can check the pH as you adjust the blend valves.
You do not need all of the water to pass through the tank, the corsex will speed the reaction, and as the tank is not used it will continue to buffer the water so the blend will help flush the higher pH at start-up. You may notice a cloudy film in the storage tank after some time, this may be due to long times of non of use of the stored water and it may require you to lower the feed pH to the storage to below 7 in order to compensate for the buffering. It should balance.
You will also have to increase your net driving pressure on the RO to overcome the permeate back-pressure the pH tank will cause (most likely no more than 5-10psi), but remember the RO is based on flow not pressure, so if it is designed to produce 1.5gpm and the pressure is 175psi at 1.5, dont make more water just becasue the pump pressure will let you. You'll over drive the membrane flux and replace membranes more often if you do.
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