# TDS "threshold"



## aquariumhobbyist (Feb 18, 2014)

Guck said:


> So I bought a cheap TDS meter and now I trying to make sense of the readings.
> 
> I know some people here measure the TDS of their tanks. What I am wondering is if there is such a TDS threshold that would more or less ring the bell and suggest water change.
> 
> ...


My small 10 gal measured 1180 ppm the other day... I couldn't believe it so I took 5 additional readings from different samples of the water and the result differed between 1170 and 1180 ppm. I have guppies, bandit cories, salt and pepper cories, amano shrimp and red cherry shrimp in there... Only plants in there are anubias sword leaf types.


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## Mariostg (Sep 6, 2014)

aquariumhobbyist said:


> My small 10 gal measured 1180 ppm the other day... I couldn't believe it so I took 5 additional readings from different samples of the water and the result differed between 1170 and 1180 ppm. I have guppies, bandit cories, salt and pepper cories, amano shrimp and red cherry shrimp in there... Only plants in there are anubias sword leaf types.


LMAO. Interesting, my 10gal also has guppies. I removed all the males, they are a bunch perv. There is also Otos and Red cherry shrimps. all semm happy.
I am gonna start to think the other 3 tanks are too low.


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## aquariumhobbyist (Feb 18, 2014)

Guck said:


> LMAO. Interesting, my 10gal also has guppies. I removed all the males, they are a bunch perv. There is also Otos and Red cherry shrimps. all semm happy.
> I am gonna start to think the other 3 tanks are too low.



I believe that guppies, due to their relatively short lifespans and their susceptibility to disease, have to reproduce quickly and with as many females as possible, to pass on their genes to the next generation. Hence, they always seem to be trying to mate (unlike fish like cichlids, which have temperature requirements, feeding requirements and so on for successful spawns). So, don't be too hard on them


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## Diana (Jan 14, 2010)

TDS for soft water fish depends on how sensitive they are. 
Something really sensitive like Licorice Gouramis or wild caught fish should be really low (100? Less?)
Most community fish whose ancestors came from soft water are usually fine with TDS between 100-500 (though 500 is a bit high). 
Most community fish whose ancestors came from hard water are usually fine with TDS between 300-1000. The 1000 is more for low end brackish water fish. 

My tap: high 200s (280 is typical). 
To raise Rams I had to go to RO. Most community tank soft water fish are fine. 
To keep hard water fish (Mollies, Swords, Guppies, Lake Tanganyika) I add some minerals, get the TDS closer to about 400. 
My brackish water tank is well over 1000, closer to about 1200-1500. I have kept Mollies, Guppies, and several specialized brackish water fish in this.


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## Mariostg (Sep 6, 2014)

Diana said:


> TDS for soft water fish depends on how sensitive they are.
> Something really sensitive like Licorice Gouramis or wild caught fish should be really low (100? Less?)
> Most community fish whose ancestors came from soft water are usually fine with TDS between 100-500 (though 500 is a bit high).
> Most community fish whose ancestors came from hard water are usually fine with TDS between 300-1000. The 1000 is more for low end brackish water fish.
> ...


Very interesting. Thanks Diana. My tap water is in the low 40s... With all that I think it will help me decide whether or not I should do water change.


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## Diana (Jan 14, 2010)

Yes, monitoring the TDS is a good method of deciding when to do water changes, and what volume. 
With the most delicate fish smaller water changes more often are better. 
With more durable fish you could let things build up a bit more, then do a larger water change. 

Delicate fish:
Do water changes such that the end result in TDS is not more than 10% lower than what it was before the water change. 
ie: if the TDS was 100 before the water change, then after it should be not lower than 90. 
Depends on what is in the new water, how big a water change you could do. If the new water has zero (RO water) then max 10% water change. 
If the new water has a TDS of 90, then 100% water change is possible (though probably not good- there are other considerations besides the TDS). 

Other things to monitor, and 'most delicate fish' suggestions:
Temperature. Not more than 2 deg F or 1 deg C up or down.
GH. Max 10% lower or 15% higher. 
pH. within 1.0 of original level. (if other things- TDS, GH) are right on target, fish will tolerate more pH change than many people think.


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## Xirxes (Aug 18, 2008)

*TDS &quot;threshold&quot;*

Btw whoever quoted tap water TDS needs to know that every part of the world, and even suburb to suburb can have VASTLY differing TDS readings.

Southern California is well known to have 4-600ppm TDS straight from tap (Why no planted tank should use tap here IMO).

I've found that sub 150 is good for almost all Amazon basin types.

References: DI source-0ppm
RO-20-60ppm depending on source water
Tap- 100-700 depending on local source

TDS will increase significantly through heavy leaching substrates, addition of Calcium, metals or salts.


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## tamsin (Jan 12, 2011)

Measure after a water change to give yourself a base line and then see how much your tank creeps up over a week or so - it's going to depend on evaporation, ferts, substrate/hardscape leaching etc.

You'll then be able to work out how much to change and how often to keep the TDS steady.


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