Neptune Aquatics

What’s an acceptable TDS measurement for aquarium water?

jepoy

jepoy

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I just got myself a TDS meter and got a 15 measurement coming out of my RODI. Is this too high? Also, I’ve been having cyano issues lately.. could this be the problem?


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It "could" be but not likely. Everyone's probably about to jump on me because in this hobby we tend to be absolutists. The truth is that a TDS of 15 is just fine (even double that is usually okay) , however the truth is it's pretty easy to get it to zero with your RODI anyway. Probably just need to change the DI resin.

The reason you'd prefer it to be at zero isn't because 15 is harmful most of the time, but because you don't know what those "15" represent. What particles. So it's simply just easier to control the easy stuff.
 
jepoy said:
I just got myself a TDS meter and got a 15 measurement coming out of my RODI. Is this too high? Also, I’ve been having cyano issues lately.. could this be the problem?


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Yes. Almost certainly. If you have above 3-4 it means your membrane filter needs change. 0-3/4 is more on di resin
 
Ranjib Dey said:
Yes, but if this is coming out of ro/di system then this means the unit has issues
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Probably. Depends on what the ppm is going in tho. I'd like to think 15 isn't 2-3% of starting ppm, which should then get absorbed by the di resin even it it was. My water in Santa Barbara was 660 out of the tap.
 
Coral reefer said:
Probably. Depends on what the ppm is going in tho. I'd like to think 15 isn't 2-3% of starting ppm, which should then get absorbed by the di resin even it it was. My water in Santa Barbara was 660 out of the tap.
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Hmm, i used to think that irrespective of what goes in, membrane filter should filter out anything above 1 micron ( differs based on type of membrane filter) , which mostly boils down to less than 7-5 ppm
 
Yeah I would be trying to get as close to zero if I were you. What is your starting TDS? You may need to change out some media, or if that doesn’t work, add another stage.


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I have a 6 stage RODI that I’ve had for 7 months. The activated carbon, carbon block, and sediment I just replaced last month. I had an extra DI filter and so I replaced that too, even though that was supposed to last a full year along with the post carbon and membrane.

Maybe I’ll replace the post carbon and membrane as well to see if that brings my TDS down.

Btw, TDS on Morgan Hill tap is 350 [emoji15]


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Ranjib Dey said:
Hmm, i used to think that irrespective of what goes in, membrane filter should filter out anything above 1 micron ( differs based on type of membrane filter) , which mostly boils down to less than 7-5 ppm
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Your prefilters should filter out larger particles (based on rating)... on average, but some can get through. However they most of those particles don't register on a TDS meter unless they have some electrical conductivity between them, carbon will get your chlorine and other molecules out. The membrane will filter out anywhere between 93 to 98% depending upon a number of factors (water temp, pressure, etc). TDS of 15 means either no resin or exhausted resin, either way means either high TDS going in, or time to replace your RO membrane which have life spans anywhere from 2-5 years.

As for being the cause of the cyano, I'm sure it's not helping, but there's a good chance it's not the sole cause. Low flow & overfeeding often are bigger culprits (overfeeding does not just mean food goes uneaten, too many fish means too much food by default)
 
sfsuphysics said:
As for being the cause of the cyano, I'm sure it's not helping, but there's a good chance it's not the sole cause. Low flow & overfeeding often are bigger culprits (overfeeding does not just mean food goes uneaten, too many fish means too much food by default)
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Back in April I went on vacation for a week and had an auto feeder feeding my tank. What I didn’t realize was that I accidentally set the auto feeder to feed twice a day. I’m pretty sure that’s what kick started the cyano, what made me suspect my RODI water was when I finally decided to use chemiclean, it got rid of about 80% of the cyano, but as soon as I did a 20% water change the cyano was back in full force the following day.


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jepoy said:
I have a 6 stage RODI that I’ve had for 7 months. The activated carbon, carbon block, and sediment I just replaced last month. I had an extra DI filter and so I replaced that too, even though that was supposed to last a full year along with the post carbon and membrane.

Maybe I’ll replace the post carbon and membrane as well to see if that brings my TDS down.

Btw, TDS on Morgan Hill tap is 350 [emoji15]


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I’m in South SJ and my TDS can hit 425 out of the tap during certain months. 0 tds our of my RO/DI.

Are you using a booster pump? The membrane needs a certain pressure to be effective. How much the membrane filters out can make a high difference. Mine are 99%. Common ones are 96% which exhausts your DI faster.


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Vhuang168 said:
I’m in South SJ and my TDS can hit 425 out of the tap during certain months. 0 tds our of my RO/DI.

Are you using a booster pump? The membrane needs a certain pressure to be effective. How much the membrane filters out can make a high difference. Mine are 99%. Common ones are 96% which exhausts your DI faster.


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No I don’t use a booster pump, but I will look into it now. Thanks!


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When I started my first tank, my house already had RO water for drinking but no DI so that’s what I used for about a year before upgrading. My tds was in the 20’s that whole time. Is it possible your tds meter could be malfunctioning?
 
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