RODI water causing problems?

[crankbait09]

In another thread I started, I was asking about Cyano bacteria. I was asking if it could be transferred from one tank to another by means of frags. One thing lead to another, and we were then trying to figure out what caused it to begin with.

I did a water change yesterday, and as I was refilling my water bins back up, preparing for the next one in 3 weeks, I checked the TDS meter. I saw that TDS 2 was at .17ppm (membrane meter), and that TDS 3 was at .08ppm (Filter output). The incoming water, from the street, measures in at around 180-190ppm. I have always had problems with these filters needing replaced sooner than the average time frame. When I saw these numbers, that raised some red flags, but then I thought, theres no way these filters need replaced this soon. Well, not the filters, but the actual membrane. The filters were replaced in August of 2018. So those are due for a replacement. As for the membrane, that was replaced in March of 2018. BRS mentions the membrane could/should last a few years. well, I'm at a little over a year. I seem to replace this membrane once a year.

Still not sure if this is the leading factor to the cyano, BUT, now I'd like to know why this membrane needs replaced so often.

Here is a diagram of how I have the RODI system plumbed. Anyone see anything that raises a red flag?

[reefgeezer]

Two things come to mind: 1) What is the accuracy of your TDS meters; and 2) When was the DI resin replaced?

Many times, digital meters are really not accurate enough for the last decimal place to have any meaning. DI resin is the consumable in the system. It will need replacing every so many gallons depending on the output of your RO unit and how often your cycle it.

[crankbait09]

I replaced the DI Resin when I replaced the other filters in the system. I do them all at once.

I am running a 75maxx RODI unit on my 170 gallon set up. (130 dt + 40g sump)

[Uncle99]

Minor TDS readings below 3ppm will cause no problems in your system.
The membrane removes the 95-99% of the TDS and the resin, the remaining 1-5%.

As noted above, most of the hobby grade equipment will only be somewhat accurate.
Your numbers may just be that inaccuracy.

In my experience, cyano appears in unstable and/or immature tanks or when one nutrient is much higher than the other, which again, can be in a newer tank set up.

Simply flow changes, and removal is the easiest, it will eventually go away.

Membranes last longer when they are not allowed to dry out....I have incoming water in your range and my membrane is two years old now.

The sediment and carbon I change every 6 months because they are cheap.

The DI resin I change when final TDS goes over 3-4 PPM

Missing a line from sediment to carbon...

[mcgyvr]

huh?
Your rejection rate at the membrane is 99+%..
Its most certainly not bad at all..

None of your filters or resin need to be replaced at this time.. All are totally fine..
As stated many wait till TDS is 2-3+ before changing DI resin..
Sub 1 TDS levels are not a problem at all..

[crankbait09]

well, ok then.

It has always been at "0", so slacked off on checking the numbers. It had always remained consistent. Until now. When I didn't see "0", I went in to stress mode.

[reefgeezer]

Originally Posted by crankbait09

I replaced the DI Resin when I replaced the other filters in the system. I do them all at once.

I have a 50 Gal/day cheap-o unit w/. I probably make 100 gallons of 0 TDS water per month. I replace RODI when the output TDS reads 1 ppm after the unit has ran for a few minutes. My meter reads in whole numbers so the TDS could be anywhere above 0 to maybe even 2 or 3 ppt. I have to change RODI w-a-a-a-a-y more often than the sediment or charcoal filters and particularly the membrane. I use color changing resin and it usually starts to show elevated TDS before all the resin changes color.

[mcgyvr]

Originally Posted by reefgeezer

I replace RODI when the output TDS reads 1 ppm after the unit has ran for a few minutes. My meter reads in whole numbers so the TDS could be anywhere above 0 to maybe even 2 or 3 ppt. I have to change RODI w-a-a-a-a-y more often than the sediment or charcoal filter.

You mean DI not both RO and DI...

[reefgeezer]

Yea... sneaking in posts at work limits proof reading time!

[bertoni]

RO membranes work best if they run for a significant amount of time non-stop. How is the pressure switch to the water bins working? Are the bins feeding an auto-topoff system?

[crankbait09]

the bins do not feed an ATO. The bins fill up, one if for salt, and one is for top off. But I top the water off manually. So the RODI unit never runs, till it's time to fill the bins. And that's about 40-50 gallons at a time, when done. (roughly twice a month)

[bertoni]

Well, that was my last useful idea.

[bnumair]

most of the tds 2 point or 3 point meters are adjustable. you can buy a calibration solution for them and calibrate them, I have a feeling its just a calibration issue on the TDS creep.