Double-Take On Total Dissolved Solids Metre

[Kaidonni]

I decided to use my Total Dissolved Solids metre this evening, haven't tested for about a month. It was reading in the 240-260ppm range...with the 'x 10' displayed. I'm sorry, but that somehow doesn't seem right - it's suggesting my tank has ~2400ppm TDS? Sorry, I honestly can't believe that! The icon wasn't flashing, but that doesn't make this any less...concerning? I tested a glass of tap water, about 265ppm, no 'x 10' icon at all. It still can't be right.
 
My White Cloud Mountain Minnows are swimming around absolutely fine, all other tank parameters are great - ammonia and nitrites are 0, pH ~7.5, nitrates as best as I could read with the fading light are between 20-40ppm on the API test (my eyes wanted to say roughly around 30ppm, it did look the closest fit against the chart, but it could have been 35ppm or higher, or also lower - I take the nitrate tests with a pinch of salt). I did feed some microwaved pea earlier in the week - it was mushier than normally defrosted peas - but I can't believe that or anything else could have pushed up my TDS by 2100ppm from when I last tested (~300ppm earlier in July, around the 11th/12th). I use a little bit extra of Prime in each bucket when I do my weekly 50% water change - a few extra droplets per bucket. I temperature match to a degree, so that means using warm water, but still...this seems more than a little excessive. It doesn't add up, even though the 'x 10' icon is only there when I dip the TDS metre in the tank, and not when I test tap water...
 
Unless it's the aquarium salt. I dosed at 1.5g/litre (75g, 50 litre tank) on Sunday. That might explain it... I only just thought of that as the possibility!

 

[TwoTankAmin]

Salt will raise TDS, but not by that. Maybe clean the tester, recalibrate it and test again?

 

[RRaquariums]

If the tester wasn't cleaned between using it last the water that was left on it will dry and all the solids will end up as a thin layer on the testing screen giving you a wrong reading as TTA said clean it recalibrate it and try again. If it's still giving you the same answer then your tester may be going bad. Have you added any new decorations since the last time you tested the water? When was the last time you did a water change and how big was it? and did you use well water or city water?
Sorry for all the questions just in this case it could be a lot of things.

 

[Kaidonni]

Well, it's something funky throwing the reading out - including the salt - because the fish are perfectly happy. A quick bit of research and 500ppm looks like it'd be pushing it for fish health, so it's hardly a genuine water quality issue (if something serious was happening, I'd expect at the levels I'm seeing, the fish would already be dead). I could try cleaning it with straight tap water to see if that helps lower the reading, but it seemed to register the glass of tap water just fine at 265ppm.
 
Last water change was last Sunday, a little under 50% (50 litre tank, changed about 23 litres - normally I change between 24-26 litres weekly). I live in the UK, it's not well water (tested, that's coming in at 265ppm). No new decorations, I just removed a plant on Tuesdat because of a blue-green algae (possibly false) alarm. I didn't wash my hand and arm as thoroughly as I normally would, but I don't think any soap from my earlier wash that night would have done anything. I wouldn't think the one pea I fed on Tuesday would have had any effect (just hoping that, as I used a bowl that had been washed up in soapy water/fairy liquid in previous weeks, and covered the peas with tap water in the bowl - using a spoon that had probably also been washed up in soapy water/fairy liquid in previous weeks - that I didn't introduce any contaminants into the fish); nor the less well prepared pea on Saturday.

 

[RRaquariums]

Well honestly I'd say it's a probelm with the tester then but still hard to say. If the fish look fine and everything else seems ok then I'd not worry about it.

 

[Kaidonni]

After my weekly ~50% water change (26 litres this time, or thereabouts), I gave the TDS metre a quick wash in tap water, a very quick dry and tested again. It gave me ~1140ppm as the result - I haven't replaced any of the aquarium salt. The readings are about half of the previous readings of ~2400ppm.
 
There might still have been some tap water on the metre in the case of the first test that I took right after cleaning the tank - hope the fish are fine, although I assume they should be due to my use of Prime and the fact that there'd only be trace amounts of chlorine on the metre, of which those would be evaporated quickly in the environment of a filtered tank that also has an airstone. By the time of my tests this evening, there probably wouldn't be anything left on the metre, and again, those trace amounts would likely be evaporated quickly in the tank.