Water Softener and RO/DI Unit

[pogodzib]

I'm building a new house and was wondering if the RO/DI unit should be hooked up before or after the water softener. Everywhere that I read says that the water softener should be hook up before the RO/DI unit to make the RO/DI unit's cartridges last longer. One of my local reef club members hooked up his RO/DI unit after his water softener and had nothing but troubles until he moved his RO/DI unit back to before the softener. I'm thinking that since water softeners soften the water by replacing calcium & magnessium with sodium, some of the sodium may have been getting through his RO/DI unit, thus causing his problems.

FOR THOSE OF YOU WITH WATER SOFTENERS, Do you have your RO/DI unit hooked up before or after your water softener and which way would you recommend?

 

[hansmatt]

bump for a tag-along!

 

[pleaselaunchme]

I'm not 100% sure about this, but I am of the understanding that RO membranes, at least filmtec anyway, are desalination filters, and as such I have a hard time believing that sodium was getting through the filters.

http://www.dow.com/liquidseps/prod/app_home.htm

According to Dow, sodium is reduced/rejected by their membranes. My gut feeling is if there really was sodium leaking through his membrane in enough quantities to cause problems, it would be a membrane problem.

To answer the question though, this is taken from http://www.remco.com/ro_quest.htm, and refers specifically to industrial RO:

Q. Is any pretreatment required?

A. There are various pretreatment configurations that will work on the front of an reverse osmosis water system. Part of the selection is based on the capabilities and experience of you maintenance staff. The better preventative maintenance you have, the easier it will be to maintain a chemical addition system. Chemical metering systems require more daily maintenance and calibration to insure consistent operation. Fixed bed systems such as softeners and carbon beds require little daily maintenance.

Water must have a very low silt (solids) content to keep the membranes from plugging up. This can be accomplished by removing the solids or keeping them in suspension while passing through the system. Chemicals can be added to the incoming water to keep the solids in suspension or efficient filtration can be used. We prefer to remove all solids before the system, which results in the lowest rate of membrane plugging.

As the water passes through the reverse osmosis system, the ionic content of the reject stream increases as water permeates the membranes. This increase in TDS can results in calcium and magnesium (the hardness ions) precipitating out in the system and plugging the membranes. Again, either the Calcium and Magnesium can be removed or a chemical can be added to keep them in solution. We prefer using a water softener to remove the hardness ions and replace them with sodium.

Chlorine must be removed for thin film membranes and should be minimal for CTA membranes. Either it can be removed by carbon treatment or reduced with a chemical addition of sodium metabisulfite. The carbon is preferred because the chemical addition can enhance bacterial growth in the system which can plug the membranes.

HTH,
Ben

 

[HowardW]

I've been told that RO membranes love water softeners and it will make them last longer. I would always install the softener upstream of the RO/DI.

 

[redox]

Its not always nessesary to have a softener before an RO, it really depends on how hard your water is. I use one before my ro because my water is hard and even if it wasnt I still would have a softener just because I like the way it feels in a shower. But as an answer to your ? ,yes it is a good idea to put a softener before your RO. RO membranes have a good track record for sodium rejection. plus its good for your skin

 

[pogodzib]

The water in our area is hard and it seems like almost everyone that lives in this area has a water softener. In my current house, I don't have a water softener so I've never needed to worry about the best way to hook up the RO unit, but our new house will have a softener.

 

[redox]

well if your water is hard then the softener will prolong the life of your RO membrane.

 

[gary faulkner]

We have very hard and acidic water. My water treatment system consists of a water softener, acid neutralizer, and bleach pump.

First a small quanity of household bleach is added to the water then the water passes through the softener then through the acid neutralizer.

This turns really bad water into excellent drinking, bathing water.

To answer your question, the RODI is after the softener.

 

[deanchi]

I have a water softener at the main, and my RO/DI is in my bathroom. I've been using it this way for quite some time without any problems.

Also, I filled my most recent reef tank with water treated with potassium chloride then RO/DI. About 5 months ago, I switched to sodium chloride. So all my recent top off water are treated with sodium chloride then RO/DI. And there hasn't been any problems either.

My understanding is that the RO membrane removes up to 96% of all dissolved solids from the water, whether it be potassium or sodium chloride.

 

[rbursek]

I have very hard water here, I have done it both ways, myTDS runs higher on the RO/DI in when it is using the soften water.
Bob

 

[AZDesertRat]

Definitely put the RO on softened water, it does much of the work for it. If used in conjunction with good prefilters and carbons it will greatly extend the life of the membrane.

 

[Buckeye Hydro]

Remember that it is primarily calcium and magnesium that form the scale on the membrane - these are removed by your water softener. So as AZ Rat stated - supply softened water to the RO unit.

 

[rbursek]

Buckeye,
I have a TDS meter, the inlet and outlet of my RO/DI runs higher if I am using soften water compared to non soften, my well water is off the charts as far as calcium goes so I do not understand.
Bob

 

[Buckeye Hydro]

The softener replaces your Ca and Mg with Sodium - so it doesn't really lower tds - just swaps Na in and Ca/Mg and other cations out. Just as softened water feels "slimey" to the touch - the Na slides through the membrane and into the waste water.

What is your well water TDS?

 

[rbursek]

buckeye,
on soften after a 5 micro string and a ac filter it is 401, non soften same point it is 378.
bob

 

[Buckeye Hydro]

Although the tds may be a little higher, the RO membrane can deal with the sodium better than it can deal with exposure to high Ca and Mg.

 

[rbursek]

BE,
thanks for that info, I will switch back to soften water, just needed an expert to confirm that!
Bob

 

[wooden_reefer]

This question is answered without reference to fish keeping. The RO member would last longer if the inflow water is low in Ca, Mg. The general water companies such as Rayne or Colligan will say so.