Help with TDS

Nick72

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Ok, I just bought a TDS meter.

Bottled Water = 108

Tap Water = 54

Aquarium Water = 546

I don't know much about TDS, but I think that's bad.

My aquarium is 18 months old and moderately planted.

I dose EI ferts for N, P, K, Ca, S, Mg + CSM+B, plus Fe.

This reading is 2hrs before the weekly water change.

Any one able to advise me on what 546 means in real terms, beyond just bad?
 

Nick72

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Total dissolved solids (TDS) is a measure of the dissolved combined content of all inorganic and organic substances present in a liquid in molecular, ionized, or micro-granular (colloidal sol) suspended form.

https://en.wikipedia.org/wiki/Total_dissolved_solids

Ha ha, Yes I knew that much.

What I'm asking is, and I guess it's my fault for not saying it correctly above, what is a healthy TDS reading for a planted aquarium.

What TDS reading should I be aiming for. Or lowest healthy through to highest healthy (range)?

Is 546 TDS over the healthy high range?

What is likely to be pushing it so high?

Does CO2 get counted in TDS?
 
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Nick72

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Sorry @Witcher , further reading of the Wiki and I came across this :

Most aquatic ecosystems involving mixed fish fauna can tolerate TDS levels of 1000 mg/l.

Freshwater is water with a TDS of between 0-1000

So this would imply that my reading is about in the middle of this, so my water is fine???
 

jaypeecee

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Hi @Nick72

That's a high reading relative to my tanks. A TDS of 546ppm equates to 853 microS/cm. None of my tanks are over 300ppm TDS. But I tend towards softer water. It all depends on what you are keeping.

JPC
 

Witcher

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Ha ha, Yes I knew that much.

What I'm asking is, and I guess it's my fault for not saying it correctly above, what is a healthy TDS reading for a planted aquarium.

What TDS reading should I be aiming for. Or lowest healthy through to highest healthy (range)?

Is 546 TDS over the healthy high range?

What is likely to be pushing it so high?

Does CO2 get counted in TDS?
I'd say it depends on what you're aiming for. If you keep plants coming from soft and nutrient poor waters and you keep them in these conditions, TDS should be rather low (because of low content of Calcium, Magnesium, ferts etc.). On the other hand if you keep plants which like more hard water, you'll aim for higher TDS (again amounts of Ca, Mg will be higher etc).
Plus amounts of ferts you add also counts for additional TDS. If you're in the middle and your plants and fish are doing ok, it's nothing to worry about.

You could be worried only if before water change your TDS will be the same like after water change plus dosed ferts - that would mean your plants are not consuming anything.
For example, let's say that you've changed your water, but haven't dosed ferts yet and your water is 100 TDS. Then you dose your ferts and your water goes up to 500 TDS (edit: however I'd agree with Darrell that it's a lot of ferts). If at the end of the week TDS is close to 100 you're perfectly fine, if closer to 500 than there are some problems with plants not consuming what you've dosed.

CO2 is in gaseous form so it doesn't counts.
 
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dw1305

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Hi all,
I don't know much about TDS, but I think that's bad.
Total dissolved solids (TDS) is a measure of the dissolved combined content of all inorganic and organic substances present in a liquid in molecular, ionized, or micro-granular (colloidal sol) suspended form.
It is quite a lot of extra ions. The meter doesn't <"actually measure ppm TDS">, it just measures the ions (as a conductivity measurement) and estimates the ppm TDS as defined by @Witcher.

I would definitely be adding less salts and <"changing a bit more water">.

cheers Darrel
 
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JoshP12

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Hi @Nick72,

TDS is one of those things like pH - absolutely meaningless but extremely powerful ... which makes no sense. It is powerful (and informative) if you know what is causing your TDS readings to go up and down. It's quick check.

I can illustrate with an example. My tap water comes out at about 80. My TDS of my WC water is about 180 (I remineralize it up). My tank probably sits around 220? Over the week, my tank goes to 280ish? ... why? Ferts (and other byproducts) - I know this because I dose it, so I am not alarmed when I see that number. If I saw it at 400, I would start to question the health of my tank and wonder what I did to trigger it. Some people use TDS as a measure of when to do their water change - because they know what it causing the increase. The other day, I tested some water at a cottage. My TDS came out at 350, so I thought "the water can't be that different from my tank" - when I tested it (see my disclosure below), I saw the KH around 15 and the GH around 21 -- My tank is about 3 and 6, respectively. What caused the difference? My ferts, my sulphates, all that other junk that I put in/gets created.

What do you aim for? I think it depends on the water you put in and the water at the end of the week :).

EDIT: and then all the comments that were put while I was writing this are great in addressing how to read the reading and what to do.

Josh



** My disclosure: I understand the uselessness of these tests but when it's all I got and merely for fun, I rolled with it -- PLUS with a discrepancy so high I think it illustrates my example.
 

Nick72

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OK. Thank you all.

I'll do a water change as scheduled today, and check TDS several times this week to see how it changes.

I might come back after that if I have more questions.
 

Nick72

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@dw1305

I can't change much more water as I'm already doing 70% Weekly water changes.

But yes I do add a lot of Salts, probably more Ca and Mg than most.

I'll think about reducing this.
 

Witcher

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When CO2 is injected into the aquarium water, it forms carbonic acid. As this is electrically-conductive, it will affect your TDS reading.

JPC
This may be actually quite confusing - we are measuring solids by measuring their conductivity - and some gasses may distort that.
 

jaypeecee

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Hi Folks

I wish these meters were not called TDS meters. As @dw1305 rightly points out, they don't actually measure Total Dissolved Solids. How could they? That requires driving off the water and then weighing the residue. They measure electrical conductivity and then take a guess! TDS meters are a proxy at best and plain misleading at worst. They do require some knowledge of water chemistry in in order to use them properly.

JPC
 
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X3NiTH

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Looks like you are accumulating something at a rate of 1ppm per day. If GH and KH have remained stable through this time (18months) then at a guess one of the main candidates would probably be K accumulation. If Nitrate trends upwards over a weeks dosing then I would suggest lowering how much you add via KNO3 (assuming this is the main source of K) if the plants still need the increased amount of Nitrogen then you can add it via MgNO3 or CaNO3. If perhaps you are using Potassium Carbonate to increase KH then swap to Potassium Bicarbonate to limit the amount of K added to increase KH.

I wouldn’t overly obsess about the TDS, yes it’s high via dosing but it’s a slow accumulation if you change more water weekly you should be able to reduce the rising trend.

:)
 

Nick72

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Thanks all for the above.

That was an interesting water change.

After water change - 228 TDS

After Prime, Excel, 2 tsp of K2SO4 (and yes this made my PH drop from 6.8 to 6.2 as normal - who knows why), 4 tsp of Epsom Salts, and 2 tsp of Gypsom - 515 TDS (also been hanging 2 small bags of crushed coral over the side of the tank for 30 minutes - I take it out after 20 hrs).

I'll add some KNO3 and KH2PO4 in the morning and no doubt be back up to where I started.
 

jaypeecee

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Hi @dw1305
It is less than 1% of ~30ppm, so I think you can ignore it.
I'm confused about the 1% figure. At pH=6.5, for example, approx. 50% of the DIC* is in the form of bicarbonate so doesn't that mean the other 50% is hydrogen ions? To be honest, I would need to check this out by running a test and I simply don't have time. At the end of the day, I suspect that the effect of CO2/carbonic acid is not likely to be an issue unless the tank water is very soft.

*DIC = dissolved inorganic carbon

JPC
 
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