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Best way to make soft water??

1259 Views 6 Replies 6 Participants Last post by  apuhl20
We have very hard water in our area, so we have a whole house (salt) water softener for the house. I have the option of using soft water or hard water for my new fish room and everything for the tank. I will need a good amount of water, 300g display with sump and eventually additional tanks. So with that there are 2 questions.

Will an RODI unit soften the hard water sufficiently to house soft water species? Discus etc

Or would I be better off using the RODI on the soft water supply.
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If using an RODI unit- hook it up after your water softner. This is the recommended approach by Bulf Reef Supply and most others. I used to have my RODI unit plumbed before my water softner. I was blowing through membranes consistently in under 12 months. Remember, you will still need to adjust both GH (calcium, magnesium) and KH (baking soda) for your RODI water.
An RODI unit will strip EVERYTHING out of the water. You will need to re-mineralize it, even with discus. Use the RO unit after the softener, the membranes will last longer. Out of curiosity, how hard is your water? I have a GH of 11-12 and KH of 7, but I keep softer water fish just fine. Discus can be fairly adaptable. Chicago Discus is considered one of the best places to buy discus and they raise them in chicago tap, and that stuff is pretty hard and alkaline.
If using an RODI unit- hook it up after your water softner. This is the recommended approach by Bulf Reef Supply and most others. I used to have my RODI unit plumbed before my water softner. I was blowing through membranes consistently in under 12 months. Remember, you will still need to adjust both GH (calcium, magnesium) and KH (baking soda) for your RODI water.
Agree 100%. RO after softener. Don't use the softener water without the RO unit, it just trades calcium and magnesium for either potassium or sodium depending upon what you load the brine tank with.

If you can measure accurately, you could use a mix of RO water and water from the well or street (bypass the water softener) in appropriate quantities to get the hardness you want. That assumes that there are not other impurities or minerals in your source water.
A good RO/DI unit with as many stages as possible will help a lot as the above posters have said. With a 300 gallon display it's not worth it to skimp on the RO/DI. Get the biggest you can with the best ratio of purified to waste water as possible. It won't be cheap, but it will save headaches in the long run.
Just sharing my regret. I got a 150GPD melev Reef unit with a booster pump open box (retail is $300). My TDS pre softener was 800 post is 670. The membrane only kicked it down to 80-160 with something like an advertised 93% rejection. I burned through one DI resin in under 50 gallons purified water. I replaced all my 5 micron prefilters with .5 spectrapure water filters and literally saw post membrane TDS of 3 and it flashed to 2. Which is like 99.6% rejection. Usually it's around 6-7 with a psi of 98-100.

Moral of the story I suggest you check your TDS before you buy a unit. Also look at chloramines. The chloramines need a smaller carbon filter and the TDS is going to determine how good of a RO membrane you'll need. So you'll know how much DI resin you'll burn through.

With hard water usually you'll run a higher water/waste ratio but if you have a softener idk if you'll need to.

I'm saying all this because I use my RODI for my saltwater tank. Have the maxcap DI and silicabuster DI to help reduce silicates that are hard to remove.

Id rather get 1 really good RO membrane with 1 DI then an medium membrane and 2DI. 1tds vs 2tds is literally the difference of the DI filter lasting twice as long.
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My RODI is the one I used when I had my 400 gallons of reef set up. It ran alot of water through it and kept the tds at 0 for months at a time. I was just seeing if people preferred it pre softener or post and if there were benefits to either.
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