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Hey everyone,

I'm in the process of buying a house that has very hard water but also uses a water softener. As I have planted tanks I'd prefer to remove sodium from the softened water before putting into my aquariums. I've decided to split my outdoor hose line (which uses the regular hard water) and make it accessible to my sink as well as using some RO/DI filtering on the soft water to cut down on the mineral hardness and hopefully maintain some control over the pH.

Does anyone have experience with this process? Has anyone installed an RO/DI to remove sodium ions from softened water? 

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A good RO/DI system should do what you want on either water line, the hard water from the hose tap or the softened water from the water softener. I've considered using an RO/DI system but my well pump has a 20/40 pressure switch on it (the pump comes on when the pressure drops to 20 psi and then shuts off at 40 psi.) An RO/DI system wants more consistently high water pressure than my well pump can deliver. There are booster pumps that can be added to solve that issue however. (Or I could just switch to a 40/60 pump switch.) Then there's the question of what to do with the waste water. Most RO/DI systems create 1.5 gallons to 7+gallons of wastewater for every gallon of RO/DI water they produce. You need to get rid of that wastewater somehow. Then the RO/DI water needs to be remineralized (at least to some extent) in most cases. Add in the purchase cost, installation cost, cost of replacement filters, membranes, what to do with the wastewater, and it all starts to become more trouble than it's worth for me. I've found other ways to get around the issues with my water. 

If allowed in your community, collecting rainwater (typically very soft and acidic) to dilute your tap water from the hose might be an easier, low-cost option. 

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22 minutes ago, gardenman said:

A good RO/DI system should do what you want on either water line, the hard water from the hose tap or the softened water from the water softener. I've considered using an RO/DI system but my well pump has a 20/40 pressure switch on it (the pump comes on when the pressure drops to 20 psi and then shuts off at 40 psi.) An RO/DI system wants more consistently high water pressure than my well pump can deliver. There are booster pumps that can be added to solve that issue however. (Or I could just switch to a 40/60 pump switch.) Then there's the question of what to do with the waste water. Most RO/DI systems create 1.5 gallons to 7+gallons of wastewater for every gallon of RO/DI water they produce. You need to get rid of that wastewater somehow. Then the RO/DI water needs to be remineralized (at least to some extent) in most cases. Add in the purchase cost, installation cost, cost of replacement filters, membranes, what to do with the wastewater, and it all starts to become more trouble than it's worth for me. I've found other ways to get around the issues with my water. 

If allowed in your community, collecting rainwater (typically very soft and acidic) to dilute your tap water from the hose might be an easier, low-cost option. 

Yeah this is all stuff I've had to consider as well. There's not an easy way for me to collect rainwater into the basement where my fish room will be unfortunately. I do think the waste produced by the RO/DI system has made me rethink the best approach. There is so much calcium carbonate in the water from our town because it comes straight out of a limestone aquifer, so I need to do something to dilute that. This is where I've come to the idea of cutting the street water with RO/DI water so that I'm eliminating the excess salt content but not having to remineralize the RO/DI water. I'm thinking a 70/30 split, with the 30% being RO/DI water might be the way to go. Then I can adjust as necessary in the event that I decide to set up a Discus tank in the future to make the water softer. It's tough because the tap water from my current house is perfect so I'm having to rethink how I do water changes in the new place (and I don't see how an automatic water change system will be possible).

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It's possible to precipitate out calcium carbonate, but it would be challenging to do it automatically. You could just add a lot of snails. They need the calcium carbonate for their shells and would gladly absorb some. Granted, it might take an awful lot of snails to keep the water where you want it and then you'd have to feed the snails and manage their wastes.

Before investing too much I might just buy some bottles of distilled water ($.80 per gallon at my local Walmart) and play with that to see how it affects your water chemistry and how much or little you need to add to get where you want things to be. If a single gallon of water alters ten gallons of your tap water to where you want it or if it takes ten gallons of distilled water to get one gallon of your tap water where you want it, will help you make a wiser decision on how to move forward.

Since you have a basement and water is pulled downwards by gravity, getting rainwater into a basement isn't overly hard. Sneak a hose through into the basement somehow from your rainwater storage with a valve in the basement and then you just need to open the valve to get rainwater into your basement. Roofs collect a lot of rainwater. If your new house has gutters diverting some or all of the gutters to storage isn't horribly hard and you get essentially free, soft, acidic (generally) rainwater.

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I've been doing this for a while.  About 8:1  RO per tap.  Water here is liquid rock with a PH of 8.3.  It took a while to get the ratio right.  PH is still high 7's as the tap has a lot of buffer.   Before that I was using all RO with equilibrium and both buffers. Mixing is way easier and so far the fish don't seem to care.

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I use a 7-stage, 100 gpd RODI system with a buddy booster. 1 micron filter, 2 carbon blocks, the RO membrane, and 3 DI stages. Before using the buddy booster, I only had 40 psi, now I have 80+, which makes the RO system more efficient. I mix 2:1 RO:tap on my water changes instead of remineralizing. I have covered tanks, so I don't top off between water changes, but it's best if you need to top of to do so with only RO water. Well water is ph 7.4, 7 dkh, need to test gh I just got the kit. By adding oak leaves to my tank, my tank is 7.0 ph, 3dkh. I'm still working to bring the hardness and ph down slowly.

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1 hour ago, ererer said:

I got the RODI used and I eventually plan to use it for a couple nano reef tanks.

I've also read that it's better to run your RO system after the water softener as it's easier on the RO membrane to remove sodium than calcium and magnesium.

yeah this part is absolutely true - if you've ever had to replace things a hot water heater in a place with hard water you know how quickly that calcium can build up. I imagine the RO/DI system wouldn't work long at all with our tap water so I'm glad to hear you and others have had success removing the sodium. 

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2 hours ago, starsman20 said:

I've been doing this for a while.  About 8:1  RO per tap.  Water here is liquid rock with a PH of 8.3.  It took a while to get the ratio right.  PH is still high 7's as the tap has a lot of buffer.   Before that I was using all RO with equilibrium and both buffers. Mixing is way easier and so far the fish don't seem to care.

At what level is it considered liquid rock? I have tap water that's coming out at like 8.6 and the hardness is almost entirely calcium carbonate. I'll have to get the test kit out again but I'm pretty sure this is going to take a lot of work to reduce.

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On 3/14/2021 at 11:19 AM, Fishdude said:

(and I don't see how an automatic water change system will be possible).

Oh, it's possible alright. There are plenty of reef keepers with different types or AWC setups that all use some sort of mixing system, so I'd suggest checking out how they do it on one of their forums (reef2reef, reefcentral, etc.). Most of the time it's a combination of holding barrels, pumps, and drains, so it might not be a continuous AWC system, but you could probably set it up where it's just two flips of a switch. Some people use aquarium controllers and dosing pumps to do continuous AWC systems on their reefs. You can use float valves to autorefill holding barrels, and you could probably even use dosing pumps to remineralize your water to a certain level. It all depends on how many tanks.

You could also setup some tanks for Tanganyikan cichlids (which are fun to watch and breed readily as well) that will appreciate your harder water parameters in your fish room running straight from a pre-softened tap source.

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Just now, Fishdude
2 hours ago, starsman20 said:

I've been doing this for a while.  About 8:1  RO per tap.  Water here is liquid rock with a PH of 8.3.  It took a while to get the ratio right.  PH is still high 7's as the tap has a lot of buffer.   Before that I was using all RO with equilibrium and both buffers. Mixing is way easier and so far the fish don't seem to care.

At what level is it considered liquid rock? I have tap water that's coming out at like 8.6 and the hardness is almost entirely calcium carbonate. I'll have to get the test kit out again but I'm pretty sure this is going to take a lot of work to reduce.

For me kh is 12, dh is 15. Ph 8.3ish hard with lots of buffer

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