# TDS always increasing



## Scorchiolee666 (8 Apr 2021)

Hello

I hope you can advise.

I am a newcomer and recently set up a small 30 litre tank, I have small amount of fish and shrimp in it, it is planted and have an array of the same rocks in it .

I have 5 Lampeye Killifish, 4 Oto Catfish  and some pygmy Corys, Blue Tiger and Blue Jelly Shrimp  

I use RO water for the tank and do water changes on most days

After doing water changes the TDS does drop but it always increases after a few days, so it has gone down to just over 140 and now after  3-4 days has gone up to 279, increasing each time

I have also lost a few of the shrimp as well, but this could of been to a large water change and the impact it had on them as well as the TDS going up and being unsuitable for them 

Reading through the forums I think it is the rocks that are causing the TDS to rise all the time, as I dont think they are inert and they are leaching minerals, I did purchase them through a well known aquarium shop but they did not have any details related to them(they were the smaller pebble size as its a small tank) , they are a sandy/orangish color, some with white/red banded stripes around them, I did purchase without researching them first but think this could be the cause, I might do a test in bucket with a few of them with just pure RO water and see if TDS does go up

Any advise would be welcome

Thanks


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## Libba (8 Apr 2021)

Did you try the vinegar/fizz test on the rocks? I'd definitely try putting some in some RO water and see what happens. That TDS rise seems significant to me.


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## aaron.c (8 Apr 2021)

TDS will always rise, as it is a measure of all the dissolved materials in the water. That said, that is a big jump in a short space of time.

Might be worth taking the rocks out and see how you get on


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## Nick potts (8 Apr 2021)

As above, there are lots of things that will cause the TDS to raise, fertilisers are a big cause and so is rock. DO you have a link to the rock you bought?

As an example, I remineralise my RO water to 120 TDS, and in one of my tanks, the TDS can be up over 500 TDS by water change time. This is mostly from the Seriyu stone and high amounts of fertiliser, but my shrimp don't seem to mind, even when i do 80% water changes.


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## Mark Nicholls (8 Apr 2021)

I use TDS to give me a rough idea of erm total dissolved chemicals. I use the aquarium note app to keep track of changes in chemistry over the hours days and weeks. I have a baseline tap water reading and also have a baseline reading of my aquarium taken after a 50% water change. Finally, I have a baseline with EI added to tap water. As others have said, tds doesn't tell you exactly what's in the water but it WILL tell you any changes in chemistry. 
Like others, I suspect the rocks or substrate are leaching chemicals into the water.


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## anewbie (8 Apr 2021)

Well.... if it is rising by over a 100 points (you said 140 to 279) I will state with some certainty that something in your tank is disolving into the water. A simple example is if you had limestone ....
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Yes my water does rise esp after a bit of time but it usually changes by 10's - i think from memory my base is around 120 and the highest a tank has gotten after several months is around 150.
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Fyi: co2 injection will raise the tds (I think because they are measuring conductivity) but even then it will only be by 10 or 20.... not 150.


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## MichaelJ (10 Apr 2021)

I’ve had similar problems - much worse though Perplexed about extreme TDS readings

In my my case it appeared to have been a multitude of factors at play, including  WC/% frequency, fertilizer, decaying plants/waste and my RO prep routine.
I excluded my substrate from the cause by having a fair amount sitting in a 19 Liter (5 US Gallon) bucket of remineralized RO water with a circulation pump for a few days and the TDS hardly changed. 

I guess with a small body of water  (30 Liter / 8 US gallon) it won’t take much in terms of leaching rocks, substrate, fertilizer etc. to make TDS swing quite a bit.

Did you check your GH after WC, and a couple of days after, to see if the GH goes up as well? if your substrate or rocks are leaching Ca it should be detectable as an increase in GH I suppose.

I typically see a jump of about 100 ppm after a week - that number probably mainly include TDS contributing fertilizer ingredients and waste (plants decay, uneaten food etc.) I do not inject CO2.

Cheers,
Michael


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## Scorchiolee666 (18 Apr 2021)

I want to thank everyone that's replied with useful help, since then I have taken some of the Rocks I had taken out and put in demineralized RO water ( which was at about 70 TDS ) with nothing else, over the course of a week its gone up to about 105 TDS , also checked with seller and they reckon its inert , also did vinegar test and none of them fizzed at all even slightly, I think its combination of fish food, minerals for shrimp and water change and evaporation of the top water (as its open top tank), so will try and remedy some of these if I can


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## Hufsa (18 Apr 2021)

If the bucket with just the rocks and RO goes from 70 to 105 TDS that is still a significant weekly increase imo. Sellers can sometimes say whatever they feel will make you happiest to hear. Im a bit puzzled your RO water has a TDS of 70, that seems pretty high, even my tapwater comes out lower than that. It may be a combination of all these factors you list combine into an even bigger increase though


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## sparkyweasel (18 Apr 2021)

Scorchiolee666 said:


> demineralized RO water ( which was at about 70 TDS


Should that say 'REmineralised'?


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## sparkyweasel (18 Apr 2021)

Hufsa said:


> If the bucket with just the rocks and RO goes from 70 to 105 TDS that is still a significant weekly increase imo. Sellers can sometimes say whatever they feel will make you happiest to hear.


Yes, it must be your rocks, whatever the seller says.


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## Scorchiolee666 (18 Apr 2021)

Sorry it is Remineralized RO water . added this to the RO water before I add it to the Tank


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## Valodia (15 Jul 2021)

One more important point about Ca/Mg/carbonates rich rocks. 
While you keep them undisturbed, the effect will become minimal, but if you brush them with a wire brush, TDS/GH/KH jumps significantly. 

A year ago I started with a small hi tech tank, you know, RO water remineralized to 5GH, 1KH. I kept using this water for 50% weekly WCs thinking that I have now soft water heaven on earth for plants and fish. However, chasing parameters for WC water is nonsense in my case, if I brush algae from my hardscape during WC, TDS goes up 300-500 ppm as well as GH and KH. 

Last WC I cleaned all the rocks with the wire brush, used 50%  TDS 7ppm RO water afterwards and got TDS reading at 230, 3 days later I have 410ppm. Of course, some of this from ferts and waste, but the main source is leaching disturbed rocks. 

A lesson here - you might have a natural remineralizer, just don't brush it too hard.


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## Tom Delattre (17 Jul 2021)

Really helpful answers here. I might add that CO2 injection / low pH eats at limestone pretty fast, so your TDS might rise fast due to that interaction.
A question, by the way: does a significant TDS rise of, say, 50 per week (due to limestone from Seyriu stone) cause a significant change in CO2 concentration or availability? Could this be enough to trigger BBA?

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## ceg4048 (17 Jul 2021)

Tom Delattre said:


> A question, by the way: does a significant TDS rise of, say, 50 per week (due to limestone from Seyriu stone) cause a significant change in CO2 concentration or availability?


Hello,
         TDS has nothing to do with the ability of CO2 to dissolve in water. There are three parameters and ONLY three parameters that have an effect on gas solubility. 
These parameters are:
a) pressure
b) temperature
c) salinity


Tom Delattre said:


> Could this be enough to trigger BBA?


No.

Cheers,


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## Tom Delattre (17 Jul 2021)

Thanks ceg. I thought the buffer effect of calcium carbonates on the effect of CO2 on pH also meant lower CO2 availability. 

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## ceg4048 (18 Jul 2021)

Tom Delattre said:


> Thanks ceg. I thought the buffer effect of calcium carbonates on the effect of CO2 on pH also meant lower CO2 availability.
> 
> Envoyé de mon KB2003 en utilisant Tapatalk


Hello Tom,
                 Yes, many hobbyists are under this impression and this originates from a basic misunderstanding of how CO2 behaves in water. When CO2 dissolves in water a small percentage of the gas reacts with the water to form carbonic acid. The percentage is very, very small. This acid has the formula H2CO3 and about 50% of this already small amount of acid "disassociates" to for H(+) and HCO3(-).

The calcium carbonate you are thinking of is the buffering that the carbonate will have in neutralizing the acidic portion H(+).

So yes, this buffering does occur, but it only occurs to the very small percentage of CO2 that forms the acid. The rest of the CO2 remains dissolved in the water and stays as CO2.

A more detailed explanation can be found in this post which is actually discussing Potassium but was diverted to address CO2 and hard water:=> Excess of K, Na, Ca, Mg... fact or myth?

Cheers,


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## Tom Delattre (18 Jul 2021)

Thanks again ceg, that's really enlightening!

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