Hi all,
Thanks for the reply, given that i have not read anywhere what a safe band is for TDS, or even a optimum value...
There isn't really an optimal level.
TDS and conductivity
A TDS meter doesn't actually measure "ppm Total Dissolved Solids", as "Ardjuna" says it is a measure of the total compounds in solution, and you can only measure it by taking a known weight of tank water, and evaporating it to dryness. The residue that remains is the "TDS" expressed as ppm.
A useful concept to visualise TDS is to think of "evaporating to dryness":
- Sea water, in that case you would mainly get salt(s), which were in solution as inorganic ions.
- A cup of tea, where you would mainly get organic compounds like sugar, the de-natured proteins from the milk and the tannins from the tea.
Conductivity
The TDS value we are given is from a measure of the all the ions in solution, with a conversion factor applied. We measure the ions in solution using the electrical conductivity of the "water" in micro Siemens.
Usually the conversion factor used is 0.64, so 100micros = 64ppm TDS.
Pure H2O is an electrical insulator, and doesn't conduct electricity, water from an RO unit will have very few dissolved salts and will have a conductivity value of ~5 microS, hard tap water saturated with calcium carbonate would be ~500 microS and 53,000 microS for sea water (mainly Na+ Cl-).
TDS Range
I'm low tech., I keep
Apistogramma and I aim for about ~100 microS. I came to this value the same way as Jordi, I measured the conductivity when the fish had spawned successfully, and the plants
<"showed some growth">, and eventually I found that these values lay in the 60 - 120 microS range.
If you are using EI your values will be much higher (plants can only take up nutrients from solution as ions).
I aim for 120 tds and use rodi. wc if it goes over 200.
I think that is probably a good approach for Discus as well. This would be a lower dosing rate than for EI.
cheers Darrel