RODI filter Change when TDS is zero

[LittleMaui]

I replaced my RO filters and DI Resin over 6 months ago. My TDS reading post filters and DI are still zero, but I am having problems with diatoms. Is there any reason to change filters if the TDS readings are zero?

 

[wkscott]

1. Depending on how pure your source water is and how much water you make it is entirely possible to still show zero tds.

2. Are you using the TDS meter that came with your RODI system? It could be malfunctioning. You may want to get a unit similar to these on Amazon.
https://www.amazon.com/gp/aw/s/ref=...244?k=handheld+tds+meter&sprefix=handheld+tds

3. Your water may not be the source of the silicates in the tank. It can be leaching from your rocks.

 

[LittleMaui]

I have 3 meters. One post filters, one post DI and one in holding container. All zero.

 

[Opus]

You have some really good tap water if it is showing zero after the RO membrane. I would either buy a handheld to double check that number or take it to a LFS that will check it for you. If it really is that low then your DI could last for years.

 

[PatW]

I find it REALLY hard to believe that any tap water in the USA is 0 tds.

 

[wkscott]

I find it REALLY hard to believe that any tap water in the USA is 0 tds.

And you are probably right. But, that is not what was said. It's zero tds AFTER going through the RODI unit.

 

[azreeftank]

And you are probably right. But, that is not what was said. It's zero tds AFTER going through the RODI unit.

He said post filters and post DI. The one after filters is before the DI, that one I can't see being zero. That will have gone thru sediment filters and RO membrane only and I have never seen zero BEFORE the DI resin. I agree I would get a hand held just to be sure

 

[LittleMaui]

Hello. I do use a handheld tester on the water storage after the filters. It also reads zero. I'm just curious whether it's ok to continue to use filters over six months old if the TDS readings are still zero.

 

[azreeftank]

Hello. I do use a handheld tester on the water storage after the filters. It also reads zero. I'm just curious whether it's ok to continue to use filters over six months old if the TDS readings are still zero.

So it sounds like the fresh water isn't the problem. How old is the tank? What's your phosphate number? How bad are the diatoms?

 

[Water Dog]

Using your handheld, what is the TDS of your source water? Also, what GPD ro membrane are you using? That will help us determine whether your inline TDS meters are giving you an accurate reading or not.

 

[Second Shot]

You will still want to change the carbon and sediment filters. If getting 0 tds you won't need to change the DI.

 

[LittleMaui]

Using your handheld, what is the TDS of your source water? Also, what GPD ro membrane are you using? That will help us determine whether your inline TDS meters are giving you an accurate reading or not.

My Tap water is 22 TDS. The diatom is a light dusting on glass that needs wiped every other day. The diatom on the substrate slightly covers gravel in areas with less flow. I "rake" the gravel each day. The tank is 15 months old using zeovit system.

 

[Water Dog]

So if source water is just 22 TDS it makes sense that post RO is 0. My source water is 88 and I use a 75 gpd membrane at 98% rejection at 90 psi and I get 0 TDS post RO. My understanding is the the more psi you're pushing, the more efficient your RO membrane. I change my prefilter based on pressure drops. My psi after the prefilters is 90 psi, if I see it drop to 80, I swap out my prefilters. That's how I determine when to change my prefilters.

Regarding your diatom issues, how long has your tank been running? Diatoms are usually a result of silicates in brand new sand beds in newly established tanks.

 

[LittleMaui]

So if source water is just 22 TDS it makes sense that post RO is 0. My source water is 88 and I use a 75 gpd membrane at 98% rejection at 90 psi and I get 0 TDS post RO. My understanding is the the more psi you're pushing, the more efficient your RO membrane. I change my prefilter based on pressure drops. My psi after the prefilters is 90 psi, if I see it drop to 80, I swap out my prefilters. That's how I determine when to change my prefilters.

Regarding your diatom issues, how long has your tank been running? Diatoms are usually a result of silicates in brand new sand beds in newly established tanks.

Thanks. I'm using a booster pump which gives me about 90psi. I'm sure this helps. I'll start watching the psi. The tank is about 15 months old.

 

[Fishgeek88]

Do you use color changing DI? My meter will read o after DI even when the resin has completely changed to brown. I will also see a rise in silicates. I switched over to the two stage DI resins by spectra pure, but still change when the color changes for piece of mind even if the meter still reads 0

 

[LittleMaui]

I do use color changing. It's such a gradual change, I don't watch it closely enough. I'll check and change.

 

[Water Dog]

I use the two stage DI canisters from Spectrapure as well. The second cartridge is a Silicabuster. I go by the two TDS meters and if the first DI stage hits 1 TDS, it gets replaced. According to the resident Reverse Osmosis expert @AZDesertRat the color changing resins often change color well before the resin is exhausted. It's more efficient to go by the TDS readings for DI resin replacement and it saves you a bit of money in the long run as well.