jack-rythm said:Can I ask where you got that from?
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dw1305 said:Hi all,
They don't really need calibration, that is the great joy of them. Although they claim to be TDS pens (TDS is "total dissolved solids"), they really measure electrical conductivity, and then use a coefficient (some-where in the range 0.5 to 0.64) to "convert" conductivity in microS into ppm TDS, <http://www.tdsmeter.com/products/calibrationsolution.html>. If you have the calibration solution you can check the meter occasionally, but they work pretty reliably.
The meter operates on a really simple method, there are 2 electrodes and a current is passed between them. Pure H2O is an electrical insulator and what we call "water" is really a dilute solution of one or more salts. The relationship between salts (as their ions) and conductivity is linear, so TDS gives you a measure of the total number of ions.
Washing in distilled water between uses is just to flush out any ions, 4dKH solution wouldn't do, but if you don't want to buy a bottle of DI water, you could use rain water.
cheers Darrel
Yes, rain water should be low in salts, but even if you haven't got any low salts water, if you give a the probe a good swirl in the water you are testing, before taking the reading, it should be OK.Is the reason you can rinse in rain water because there is no additives in it unlike from your water supplier???
I just tested my tank water for the first time and I got a reading of 570 (my tap water reads 80). I think this is too high for CRS. EI dosing is probably increasing it.
dw1305 said:Hi all,
Yes, rain water should be low in salts, but even if you haven't got any low salts water, if you give a the probe a good swirl in the water you are testing, before taking the reading, it should be OK.Is the reason you can rinse in rain water because there is no additives in it unlike from your water supplier???
I just tested my tank water for the first time and I got a reading of 570 (my tap water reads 80). I think this is too high for CRS. EI dosing is probably increasing it.
Opinions will differ about your waters suitability for CRS, but I think we would all agree that you are right about the TDS value being because of EI. Personally I'd stop EI & go low tech. (but I don't use CO2, don't grow carpets and aren't interested in maximal growth) and use the "Duckweed Index" <http://www.ukaps.org/forum/viewtopic.php?f=27&t=21003> to fertilise your plants.
I think with regular water changes you should be able to keep the TDS around 120 - 150ppm.
I use rain-water, but have a hard tap supply, keep soft-water fish and I change about 10% of the tank water every day. I can then just manipulate the proportions of rain and tap to keep the conductivity about 70 - 100 TDS.
I don't try and measure anything else, and I just use the condition of the floating plants to tell me when nutrient levels are very low. I think this is a really easy approach to keeping shrimps etc, as it gives you tank stability and I think for the trickier fish and shrimp etc. stability is the key.
cheers Darrel
Would it help the TDS if i did not add in my ferts dry (as i do) and diluted them first in water???
AverageWhiteBloke said:Would it help the TDS if i did not add in my ferts dry (as i do) and diluted them first in water???
It doesn't matter if you dilute them once in the tank they are in and will increase the total sum of dissolved salts regardless of how you administer them.
What size of a tank are we dealing with? Dosing EI values won't increase your hardness levels by a significant amount. You shouldn't have to add magnesium so you can take that out which will reduce the amount of salts a little. RO units are more reasonably priced these days. Some LFS will sell RO/pure water but making your own will work out cheaper in the long run. If the tanks not that big API do a water purifier with resin in to strip out minerals for around £40 or you could collect rain water which seems in abundance lately If you go down the rainwater router would probably be an idea to filter it over some active carbon first. Rain water picks up plenty of other industrial nasties on the way down depending on where you live.