# Help with TDS



## Nick72 (30 Jun 2020)

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?


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## Witcher (30 Jun 2020)

Nick72 said:


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





Nick72 said:


> what 546 means in real terms



_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


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## Nick72 (30 Jun 2020)

Witcher said:


> _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 (30 Jun 2020)

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???


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## jaypeecee (30 Jun 2020)

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


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## Witcher (30 Jun 2020)

Nick72 said:


> 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.
> 
> ...



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 (30 Jun 2020)

Hi all, 





Nick72 said:


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





Witcher said:


> 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 (30 Jun 2020)

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.


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## jaypeecee (30 Jun 2020)

Nick72 said:


> Does CO2 get counted in TDS?



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

JPC


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## Nick72 (30 Jun 2020)

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.


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## Nick72 (30 Jun 2020)

@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.


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## Witcher (30 Jun 2020)

jaypeecee said:


> 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.


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## jaypeecee (30 Jun 2020)

Hi Folks

I wish these meters were not called TDS meters. As @dw1305 rightly points out, they don't actually measure *T*otal *D*issolved *S*olids. 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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## dw1305 (30 Jun 2020)

Hi all, 





jaypeecee said:


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


It is less than 1% of ~30ppm, so I think you can ignore it. 

cheers Darrel


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## dw1305 (30 Jun 2020)

Hi all, 





Nick72 said:


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


It is definitely the salt addition from the fertiliser and /or salts  added to increase dGH/dKH.

cheers Darrel


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## jaypeecee (30 Jun 2020)

Witcher said:


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



Yes. But I can only think of CO2 right now that might have this effect.

JPC


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## jaypeecee (30 Jun 2020)

dw1305 said:


> It is less than 1% of ~30ppm, so I think you can ignore it.



I'm not sure. I'll need to think about that and my lunch is now beckoning. See y'all later!

JPC


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## X3NiTH (30 Jun 2020)

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.


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## Nick72 (30 Jun 2020)

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.


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## jaypeecee (30 Jun 2020)

Hi @dw1305


dw1305 said:


> 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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## X3NiTH (30 Jun 2020)

Nick72 said:


> Thanks all for the above.
> 
> That was an interesting water change.
> 
> ...



Yep that lot would do it!


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## jaypeecee (30 Jun 2020)

Hi @Nick72


Nick72 said:


> Aquarium Water = 546
> After water change - 228 TDS



That's a big drop in TDS. Your GH and KH will have also dropped by this percentage (approx. 40%). Just something to be aware of. What fish and other species do you have in your tank?

JPC


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## dw1305 (30 Jun 2020)

Hi all, 





jaypeecee said:


> 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?


No, the vast majority of CO2 remains in solution as a dissolved gas, a very small proportion of it (0.15%) becomes carbonic acid (H2CO3) which disassociates into a H+ (proton) and HCO3- ion. 

Acids are "proton donors", you've added a proton H+ and the pH falls.

cheers Darrel


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## jaypeecee (30 Jun 2020)

Hi @dw1305 

Many thanks for your reply immediately above. I had a hunch that I was incorrect.

JPC


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## Nick72 (30 Jun 2020)

jaypeecee said:


> Hi @Nick72
> 
> 
> That's a big drop in TDS. Your GH and KH will have also dropped by this percentage (approx. 40%). Just something to be aware of. What fish and other species do you have in your tank?
> ...



Yes, that's why I added the Gypsom, Epsom Salts and hung the crushed coral over the side.

My tap is 54 TDS, KH0, GH1


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## jaypeecee (30 Jun 2020)

Hi @Nick72 


Nick72 said:


> Yes, that's why I added the Gypsom, Epsom Salts and hung the crushed coral over the side.
> 
> My tap is 54 TDS, KH0, GH1



That is _soft_ tap water! What fish and other inhabitants do you have in your tank?

JPC


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## Nick72 (30 Jun 2020)

jaypeecee said:


> Hi @Nick72
> 
> 
> That is _soft_ tap water! What fish and other inhabitants do you have in your tank?
> ...




All fairly hardy, 
1x Angelfish 
1x Pearl Gourami 
1x Panda Garra 
8x Red Eye Tetra 
3x Rummynose Tetra 

Adding 4 x Siamese Algae Eaters later tonight


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## dw1305 (30 Jun 2020)

Hi all, 





jaypeecee said:


> Many thanks for your reply immediately above.


I knew "acid rain" was a problem, but I must admit before I joined this forum I'd always assumed that all the CO2 went into solution as carbonic acid, I didn't realise that most of it remained as dissolved gas.

cheers Darrel


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## JoshP12 (30 Jun 2020)

Nick72 said:


> Thanks all for the above.
> 
> That was an interesting water change.
> 
> ...



 I’d test that TDS again right now! Sometimes Prime makes it spike while it is working - then it goes down. 

The other day, I added prime and tested TDS, went upstairs got a drink to ponder, came back down and it lowered.

I suspect it has to do with the dechlorination process.

Josh


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## hypnogogia (30 Jun 2020)

Nick72 said:


> My tap is 54 TDS, KH0, GH1


I remember the water being very soft and slimy when showering in Kuala Lumpur, and always having the feeling that soap hadn’t washed off properly.


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## jaypeecee (30 Jun 2020)

Hi @dw1305


dw1305 said:


> I knew "acid rain" was a problem, but I must admit before I joined this forum I'd always assumed that all the CO2 went into solution as carbonic acid, I didn't realise that most of it remained as dissolved gas.



I can't quite get my head around this. I think I'm having difficulty with the expression 'dissolved gas'. I guess it may be appropriate to think of carbonated drinks. Perhaps the CO2 is distributed throughout the liquid as microscopic bubbles (injected under pressure). When the cap is taken off the bottle, the pressure drops and the bubbles come to the surface of the drink. So, how does this relate to injected CO2 in our tanks, if at all? If we magnified a volume of tank water, would we see ultra-small CO2 bubbles moving around? If that is the case, then they're not really _dissolved_, are they?

I seem to recall that Clive (ceg4048) once talked about dissolved sugar cubes in a cup of tea but I haven't a clue where it was.

JPC


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## Nick72 (30 Jun 2020)

JoshP12 said:


> I’d test that TDS again right now! Sometimes Prime makes it spike while it is working - then it goes down.
> 
> The other day, I added prime and tested TDS, went upstairs got a drink to ponder, came back down and it lowered.
> 
> ...




Hi Josh,  just recheck 518 TDS so no real change.


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## jaypeecee (30 Jun 2020)

Hi @Nick72 

I apologize for unintentionally steering your thread off-course with the CO2 finer detail. I'd like to pursue this further with @dw1305 so I suspect that the best way for me to do this is via PM.

JPC


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## jaypeecee (30 Jun 2020)

Hi @Nick72


Nick72 said:


> ...just recheck 518 TDS so no real change.



Gee! This is bizarre. I presume that your main reason for using _Prime_ is to remove chlorine and/or chloramine from your tap water?

JPC


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## Nick72 (1 Jul 2020)

jaypeecee said:


> Hi @Nick72
> 
> 
> Gee! This is bizarre. I presume that your main reason for using _Prime_ is to remove chlorine and/or chloramine from your tap water?
> ...



Yes, that's right.


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## Dr Mike Oxgreen (1 Jul 2020)

jaypeecee said:


> I can't quite get my head around this. I think I'm having difficulty with the expression 'dissolved gas'. I guess it may be appropriate to think of carbonated drinks. Perhaps the CO2 is distributed throughout the liquid as microscopic bubbles (injected under pressure). When the cap is taken off the bottle, the pressure drops and the bubbles come to the surface of the drink. So, how does this relate to injected CO2 in our tanks, if at all? If we magnified a volume of tank water, would we see ultra-small CO2 bubbles moving around? If that is the case, then they're not really _dissolved_, are they?


No, if you were to dissolve some CO₂ in water and then observe with a powerful enough microscope, you _wouldn’t_ see any bubbles. If it were possible to zoom in further, you’d eventually see CO₂ molecules roaming the spaces between the H₂O molecules. There would be some electrostatic interaction between CO₂ molecules and the water molecules, which I believe is what makes it possible for the CO₂ to dissolve.

When a fizzy drink is kept under pressure, that pressure is what’s preventing the CO₂ leaving the liquid solution and becoming gas. I’m unsure of the small-scale reason for that, but it may help to imagine the CO₂ molecules hiding in the gaps between water molecules because that’s how they can occupy less volume. As soon as you release the pressure, it becomes easier for the CO₂ molecules to exit the water, and so they come out of solution and form gas bubbles. In a sense, dissolved CO₂ isn’t really a gas.


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## Jonatk (1 Jul 2020)

Hi, How much of a water change do you do? I had a similar problem last year. I have a 120x 60 x60cm tank with medium density planting. I was only doing 25% water changes and i found my TDS climbed to similar levels as yours. I sort some advice from the forum and after doing a series of water changes 24hrs apart that brought the levels right down. I then switched to 50% weekly water changes and have had no problems since.


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## Nick72 (1 Jul 2020)

Jonatk said:


> Hi, How much of a water change do you do? I had a similar problem last year. I have a 120x 60 x60cm tank with medium density planting. I was only doing 25% water changes and i found my TDS climbed to similar levels as yours. I sort some advice from the forum and after doing a series of water changes 24hrs apart that brought the levels right down. I then switched to 50% weekly water changes and have had no problems since.



I do 60% -80% water changes once a week. Always have.

When I add up each of the Salts I use for EI dosing and GH + KH buffer it is around 200ppm per week.

Then add some Prime, daily Excel, and a some organics from the plants, then it's no surprise that the TDS can reach these levels.

I'm not concerned now I understand where the ppm are coming from.  It's all additives that I want in the tank, and no one above has given any reason why this should be an issue.


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## Jonatk (1 Jul 2020)

Nick72 said:


> I do 60% -80% water changes once a week. Always have.
> 
> When I add up each of the Salts I use for EI dosing and GH + KH buffer it is around 200ppm per week.
> 
> ...


I too was chasing GH and KH numbers around by adding various products to my tank. My GH and KH figures were the same as yours. I now only add crushed oyster shell to the external filter to buffer the ph, Excel and my E.I dosing. I have gouramie, tetra, corys, hatchetfish etc. I find that the fish are happy with the water parameters and plants are growing great. Why not leave it another 24hrs and do a water change, then leave it another 24hrs and do another, but without adding everything else. Then see where your tds is.


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## Nick72 (1 Jul 2020)

Jonatk said:


> I too was chasing GH and KH numbers around by adding various products to my tank. My GH and KH figures were the same as yours. I now only add crushed oyster shell to the external filter to buffer the ph, Excel and my E.I dosing. I have gouramie, tetra, corys, hatchetfish etc. I find that the fish are happy with the water parameters and plants are growing great. Why not leave it another 24hrs and do a water change, then leave it another 24hrs and do another, but without adding everything else. Then see where your tds is.



Why?

What is the issue with a TDS of 542?

My fish are all extremely happy and healthy, my plants are now growing well, where as I struggled to grow anything before increasing the GH.

So far no one has said a TDS of 500+ is bad because?

Or you should avoid a TDS of over 300 because?

So why are you advising me to lower my TDS?


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## jaypeecee (1 Jul 2020)

Hi @Nick72 


Nick72 said:


> ...no one above has given any reason why this should be an issue.



We were still in the process of gathering the facts and advising you about interpretation of TDS meter readings. And, your TDS readings were starting to get very confusing. I, for one, wasn't at the point where I could best advise you how to proceed. Further discussion was/is necessary. If you need further help, just say and I will try to do just that.

JPC


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## jameson_uk (1 Jul 2020)

Nick72 said:


> What is the issue with a TDS of 542?
> 
> My fish are all extremely happy and healthy, my plants are now growing well, where as I struggled to grow anything before increasing the GH.
> 
> So far no one has said a TDS of 500+ is bad because?


As others have said TDS on it's own is pretty meaningless.   It really depends on what makes up the TDS which a TDS meter won't tell you.
That said, I have hard water (GH12/KH5 and TDS out the tap is ~300).   The tank runs ~340 TDS and I add a reasonable amount of ferts.   So whatever makes up the TDS is there in a reasonable amount (more than you would expect)

*Edit:* Re-read and it was confirming the reading. I see it did drop to 288 after a water change. Which means you (or something) is added quite a lot of something to the water post water change
The confusion really is that if you have TDS of 542 and replace 70% with tap water that has TDS of 54 your tank should drop to somewhere near 200 and you are saying it is still that high after a 70% water change?

Have (can) you calibrate your TDS meter?   I have had some from Amazon here which are basically random number genertators....


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## Nick72 (2 Jul 2020)

jameson_uk said:


> As others have said TDS on it's own is pretty meaningless.   It really depends on what makes up the TDS which a TDS meter won't tell you.
> That said, I have hard water (GH12/KH5 and TDS out the tap is ~300).   The tank runs ~340 TDS and I add a reasonable amount of ferts.   So whatever makes up the TDS is there in a reasonable amount (more than you would expect)
> 
> *Edit:* Re-read and it was confirming the reading. I see it did drop to 288 after a water change. Which means you (or something) is added quite a lot of something to the water post water change
> ...




There is no calibration option on my TDS meter, but it's consistent.    Tap water always 54 (+/- 3),  Bottled Mineral Water always 108 (+/- 2), tank water within 10 TDS of where I left it the day before

When my tank's TDS is 228 after a 70% water change with 54 TDS water (tap), and I then add 200ppm in ferts + Prime + Excel + GH buffer.  I then add crushed coral, and my tank settles at 515 TDS, I'm not surprised or concerned.   

I'm adding Excel every day, along with alternating micro and macro ferts, and every day my TDS is going up around 10-15ppm, I'm not surprised.

I'm sure I could bring my TDS down to around 300 very easily with just one more water change.  I suspect after several weeks it would have creeped back to the 500+ range, unless I did two water changes per week, or reduced the salts I'm adding.

Right now I can't see any reason to do either.  The salts are in their to enhance plant growth, I see no reason to dilute them with water changes or stop adding them.

Hey, I've only had the TDS meter a few days, perhaps I will notice something more sinister happening over time, but right now I'm not concerned.


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