# TDS Controller



## SvenRhapsody (Feb 3, 2006)

Well, I've got my RO unit running well now, but I need to reconstitute the water to a slightly buffered level. I'm going to run the waste water back into the container until I get about 30ppm dissolved solids which should leave it at least somewhat stable. To do this I want to hookup a TDS controller to my reservoir and use a solenoid to open up a valve. Has anyone used a TDS controller? Has anyone used a solenoid for 1/4" OD tubing? Recomendations?

Thanks,
Sven


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## rba (Aug 25, 2006)

Most city water supplies have some sort of disproportionate levels of solids plus the possibility of undesired things, maybe heavy metals. After running it through the cartridges and past the membrane it won't get more balanced. I wouldn't reuse the waste to raise the TDS of RO water. I would just use a balanced RO restorer like Kents RO Right. For such a low desired TDS you wouldn't need a whole lot. I do use the waste for some fish which don't need super soft water. I just wouldn't use it for what you described. JMO.


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## SvenRhapsody (Feb 3, 2006)

Hi,
Thanks for your input. The water does run through the sediment filter and two carbon filters. What are you concerned about their being in the water. I was liking the idea of not wasting at least _some_ of the water. I expect to go through a couple hundred gallons a week so I had assumed that a commercial RO reconstituter would be expensive. I should probably check them out to determine for sure though.

SR


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## rba (Aug 25, 2006)

There is no specific thing I have in mind. But if a sediment filter and carbon took everything out you wouldn't need RO. So the answer is the unknown, whatever the carbon doesn't absorb. That substance(s) will be in a higher porportion than if plain tap water was used to add back in TDS. And tap water has been processed which may alter it before it got to your house.

If you took your RO water and dumped in some Epsom salts your TDS would go up. But is would be extremely unbalanced water. No calcium or trace minerals. Just an example of how a TDS reading can give a distorted impression.

That's why I think the commercial products are worthwhile. Here's an example:
very soft water, 1/2 teaspoon per 10 gallons (discus)

That's 10 teaspoons/200 gallons or just 3 slightly rounds tablespoons. They describe very soft water as 80-125 ppm. You want a third of that? A tablespoon a week? And it will have a fairly neutral pH, sodium, magnsesium, calcium and potassium plus major and minor trace minerals. You can't do that with waste water.

I don't know what you plan on keeping in such bland water, 30 ppm is really really low. Not what I would call stable or buffered at all but I don't know your intent.

If you don't have a DI canister you may already have 30 ppm in the output.

Run the waste into the washing machine for the first fill or a storage tank for the toilet. Water the plants. Fill the dog's water dish. Remember, the waste is a lot nicer than tap water. I use every drop.


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