I need help with my RO/Di unit please

I got a good deal on a used Aquatic Life Twist-in 4 stages (100 gpd). The guy bought it last december and told me he only made about 7 gallons per week and his tap water TDS was 107 ppm. I calculated he made about 125 gallons of good water. This unit has an average rejection rate of 1:3.5. He lives in a different city than me but in my city the chlorine level is no more than 1 ppm. At 1 ppm chlorine, this unit will make 650 gallons of good water. So I figured I had about 525 gallons left and I made about 15 gallons so far. My tap water TDS is about 90 ppm.

At first, I noticed the unit only makes about 70 gallons per day instead of 100 (it takes almost 2 hours to make 5 gallons). I didn’t think much of it because my water pressure might be too low; I don’t have any way to measure it.

Then, after only using it 4-5 times and making about 20 gallons, today I noticed the water that I was mixing with salt was taking longer than usual to become clear. I thought the little white residues in the water was undissolved salt so I mixed it a little more and then poured it in my mixed saltwater bin with another 5 gallons that I had previously mixed. My bad, I didn’t check the TDS before doing it (saltwater is new to me, I’m learning the hard way).

Then I made another 5 gallons of RO/Di water and I noticed the same thing : tiny little white residues floating in the water. This time it couldn’t be undissolved salt so I thought it might be particles from the unit. I measured the TDS and it was at 35 ppm. The last batch of good water was 0 ppm. So this is a brand new problem that just appeared today, after doing a 5 gallons bucket.


Here are my questions :

1) what is causing these white floating residues ?
2) which cartridges do I have to change ? (The deionization cartridge has not changed color it seems. It’s still a uniform dark brown)
3) do I keep the saltwater mix that I have in my bin, which consists of 50% water with 0 ppm TDs (I think, by looking at it, but I didn’t test it before) and 50% water with 35 ppm with the white residue floating around ? I guess not, but I worked hard to make it and I’m so frustrated...

If I have to change all cartridges, I’ll be paying more than the full price and I didn’t even get all the accessories that came with it. I already had to buy one part separately. Sigh.

 

You don't really know how old that unit is and from what you're saying i say its a lot older and a chance the filters are breaking down, water coming from the unit should be pristine especially with a di resin as the last stage, you can't calculate what water you're going to get it doesn't work like that, some filters should be changed every 6 months if your not running it constantly and you find the cartridge going green, it also depends on what you are receiving from your source, tap water fluctuates as they change things, you'll also find they will not run efficiently it your psi is under 65psi your water waste is normally 4 to 1 so for every gallon you make you loose 4 by waste unless you have two menbrains inline then it can come down to 1 to 1
Your tds reading will start to go up from the unit the more water you produce, I even doubt anyone gets what the manufacturer says as there's a lot of variants to consider,
Depending what salts you use and for what purpose will dictate how fast they disolve.
I would not keep whats been made and would certainly replace every cartridge and di resin, start fresh and you know where you stand but the choice is yours

 

I would not keep whats been made and would certainly replace every cartridge and di resin, start fresh and you know where you stand but the choice is yours

Thank you for your input. That’s what I chosen to do, except for the membrane. I’ve tested it with the flush cap on the Di resin and from tap water with a TDS of 83 ppm, I get a TDS of 3 ppm when it comes out.

The white floaties are nowhere to be seen with the Di resin off, so it means my problem will be solved with brand new cartridges.

I’ve ordered the sediment and carbon cartridges before knowing the Di resin was also exhausted (it’s dark brown instead of blueish, which at first I thought it meant it was full). So I’ll go get the cartridge tomorrow at a local store, so I at least save on shipping fees this time.

 

Thats the best route to go under the circumstances.
Whats the water for as in tank/fish

 

Thats the best route to go under the circumstances.
Whats the water for as in tank/fish

It’s a 13.5 gallons Fluval Evo, my first ever saltwater tank.

It has two juvenile oscellaris in it at the moment. And one green slimer slowly dying that I’m hoping to save by switching to RO/Di instead of tap water.

Once I’ve changed 100% of the water I’ll get some inverts and maybe a goby. And more easy corals eventually.

 

The only things I know about saltwater is it needs ro and a sump if the second part is correct

 

The only things I know about saltwater is it needs ro and a sump if the second part is correct

The Fluval Evo is built with a separate part for the return pump and media. It’s like a very small built-in sump. This tank is made especially for saltwater and it’s perfect for a beginner like me.

 

Thanks for explaining, I hope it works out for you