RO System BEFORE or AFTER "Softener"

[jwcarlson]

I'm going to be setting up my RO filter here this weekend, or at least "soon".
I have an ion exchange unit "softener", I bypass this for my discus water, but I am assuming that the RO unit will remove the ions exchanged in. And am wondering if that's better than running straight tap water with calcium and whatnot in the water?

I'm leaning towards that being the right thing to do, meaning run the water through the softener and then through the RO unit.

Thanks!

[jeep]

The production of your water will be nearly the same no matter where you place the RO unit. But your membrane will last much longer if you place it after the softener.

[jwcarlson]

Thanks, Brian! That's what I expected.

[jwcarlson]

Got it set up today. Straight tap is 300 ppm. "softened" water is about 650 ppm. RO water is 2-3 ppm (no DI, just RO).
Waste water was around 450 ppm. I do not anticipate needing a lot of RO, but can I use waste water for anything?

[jeep]

I use my waste for regular discus and grow outs but I don't have a softener. My waste water is very close to my tap water in TDS, around 400 or so. This must mean whatever you're using to soften the water (sodium or potassium?) must be what's raising the TDS. If it's sodium, I wouldn't use it on discus. Potassium, I'm not sure about. Can you take a reading of your water after the softener and before the RO unit or is that the 300ppm?

[jwcarlson]

Regular tap no softener is 300. After softener, before RO is 650. It is sodium, I didn't even think of that. So I would not use it for anything fish related. My understanding is the ion exchange units basically add two sodiums for each calcium/magnesium they remove. Which would make the 300 to 650 roughly make sense.

Now wondering if I've actually got softened water going into the RO as the waste should be higher than 650 shouldn't it? Unless the sediment and carbon block are taking some of that out. Hmmm...

[jeep]

Now wondering if I've actually got softened water going into the RO as the waste should be higher than 650 shouldn't it? Unless the sediment and carbon block are taking some of that out. Hmmm...

A little of each as well as what is caught by the membrane.

[jwcarlson]

Thanks for your help, Brian!

[Willie]

A water softener just adds sodium/potassium salts to the tap water to keep the calcium and magnesium ions from precipitating out and clog up your tubes. So if the R/O gets water prior to the softener, it has less work to do and will produce much purer water. Sodium/potassium ions are dissolved and will not be pulled out by carbon block or physical filtration. The R/O filter will be 50% less effective using softened water and the membranes will last 50% as long.

The problem is that "soft water" and "softened water" are not scientific terms. Softened water is not at all soft from the perspective of an aquarium hobbyist - it typically has twice the TDS reading.

[jwcarlson]

Willie, I'm not doubting you at all. But I have not found a single source on this that says the same as what you're saying here. I guess the main thing seems to be that the "softened" (ion exchanged) water contains ions that are more easily filtered by the membrane and that they flush away better than minerals even if there's "more" of them. Which I think is exactly why the ion exchange systems help limit scale.

[Vanman]

Might be a good idea to ask the membrane manufacturer about this. I have never used RO as my water is very soft and acidic.

[jwcarlson]

I've done a decent amount of reading before posting this, but wanted to get a "discus" take just because who knows what I might be overlooking. The funny part (maybe), is that at this point I don't plan to use this for discus at all. But for my apistos.
In any event, there's some "whole house" manufacturers that double membrane warranty if the membrane is after a softener. There might be some confusing because a DI system AFTER a softener is absolutely going to deplete faster, because (as Willie notes) a softener adds additional ions.

The truth of the matter is probably that it doesn't much matter for what I'm going to use it for. It's not whole house, it's to fill a 30 gallon trash can so that I can mix some with tap water and try to breed apistos. And I'm thinking I'm going to be using this roughly 30 gallons of water like once a week maybe? It will consume more salt in the softener, but I'm not too concerned about that because basically the whole family is gone between 6 PM and 4PM... we don't use all that much water anyway. Except the nightly discus water change, but that's all straight tap water anyway.