TDS Correlation with Filter Cleanliness

[Richard Dowling]

Hi All,

Im new to the concept of TDS Reading,

I have a TDS stick now and have been having a play, checking tap water, then my aquarium water before and after water changes.

I usually see a pre water change reading of around 330 and a post water change reading of 260/270.

Can TDS be used as a method of knowing when you should do a filter media wash? I have a large filter in comparison to the tank size (15x volume per hour), presumably my filter doesn’t need washing as often as most. I wondered whether I can expect to see the pre/post water change readings rise together as the 2 week old filter matures and whether this would indicate the need to wash the filter?

It would be nice to use TDS as an indicator of filter cleanliness (if that is what its for)

 

[dw1305]

Hi all,

Can TDS be used as a method of knowing when you should do a filter media wash?

Not really, but you can certainly use it as a trigger for filter cleaning, and it is a useful indicator of when you might need to change a larger volume of water. The most useful indicator for when the filter needs cleaning is when the flows drops off.

If the TDS meter actually measured TDS (Total Dissolved Solids) it could be an indicator, but it doesn't. All TDS meters actually measure conductivity in microS, and then use a conversion factor (between 0.5 and 0.64) to estimate TDS.

Conductivity is a measure of all ions in solution, pure water has no ions (for practical purposes), and is an electrical insulator, sea water is fairly salty (about 53,000 microS), and a good conductor. Ions come from the dissolution of soluble salts, so NaCl gives you a cation (Na+) and an anion (Cl-) & CaCO3 dissolves to (Ca++) and (2(HCO3-).

If we add any fertilisers, they are only available to the plant as ions.

Conductivity rises in the tank over time as water (H2O) evaporates leave more salts in a smaller volume of water, and as the biological processes in the tank take place, converting NH3 to NO3- etc.

Planted tanks differ from non-planted tanks in that conductivity may fall over time in the tank as the plants remove ions during growth.

cheers Darrel

 

[Richard Dowling]

Hi all, Not really, but you can certainly use it as a trigger for filter cleaning, and it is a useful indicator of when you might need to change a larger volume of water. The most useful indicator for when the filter needs cleaning is when the flows drops off.

If the TDS meter actually measured TDS (Total Dissolved Solids) it could be an indicator, but it doesn't. All TDS meters actually measure conductivity in microS, and then use a conversion factor (between 0.5 and 0.64) to estimate TDS.

Conductivity is a measure of all ions in solution, pure water has no ions (for practical purposes), and is an electrical insulator, sea water is fairly salty (about 53,000 microS), and a good conductor. Ions come from the dissolution of soluble salts, so NaCl gives you a cation (Na+) and an anion (Cl-) & CaCO3 dissolves to (Ca++) and (2(HCO3-).

If we add any fertilisers, they are only available to the plant as ions.

Conductivity rises in the tank over time as water (H2O) evaporates leave more salts in a smaller volume of water, and as the biological processes in the tank take place, converting NH3 to NO3- etc.

Planted tanks differ from non-planted tanks in that conductivity may fall over time in the tank as the plants remove ions during growth.

cheers Darrel

You seem to really know your science Darrel! What do you do for a living?

I did a diploma in water engineering but unfortunately it appears my brain is sieved so the chemistry side hasn't lived long in the memory!

Sent from my XT890 using Tapatalk

 

[dw1305]

Hi all,

You seem to really know your science Darrel! What do you do for a living?

I look after a small teaching and research lab. at one of Britain's newer universities. We used to do a lot of waste water work and ecology/ecological consultancy, but in more recent years I've had psychologists and human biologists in as well.

A larger proportion our work is now computer based as well, with increasing use of Apple Macs & tablets.

cheers Darrel