Using a TDS meter to gauge EI

Tom Barr

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Jan 23, 2005
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Rather than testing and using colormetric test which tend to be inaccurate
and you still cannot test every nutrient, this a single easy to use meter
that can correlate a good time to change the water.

This an allow multiple tank measurements rapidly and easily.
They are also cheap and accurate, 20-30$ on ebay.
For folks worried about build up using EI, or those that desire longer ,
small water change intervals, this might be a good way to go about it.

The TDS does not test anything specific, just total build up.

If EI is done and no/fewer water changes are done, dosing Ca/Mg/SO4 will
become part of the routine and can be accounted for individually. SeaChem
EQ works well for this.

You can measure the build up of things like NO3, K, PO4, GH., Traces also,
by measuring __before and after__ dosing of these nutrients if you add them
individually and then monitor them over time.

So you can measure things individually ................
From there you have an idea of how much TDS is added from each dosing of
each nutrient mix.

This use is far simpler than testing individually for NO3, K+, PO4, Fe and
the meter reading is fast, minimal calibration of chemical knowledge
required, cheaper and easy.
While I like my $$$ testing spect, this has some very user friendly
application for only 20-30$.

Regards,
Tom Barr

PS:

There are other methods to reduce the build up that require no test kits,
but simply consistent dosing volumes over 3 week intervals for each
nutrient of interest. After a few weeks of doing this, folks know what each
deficiency looks like and can dose accordingly.
You can go down the line and isolate each nutrient while adding excess nutrients for the others, then bump that amount up to the previous highest amount.
 

chubasco

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Jan 24, 2005
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Re: Using a TDS meter to gauge EI

A bunch of us in the AKA (due to Wright Huntley's urging) bought the Hanna Instruments TDS meters when they were on sale for $14.95, I guess it was 5 years ago. Yep, handy little tool that gives you a quick "snapshot" of what's going on in your tankwater when it comes to increasing dissolved solids. Some
killies don't do well (breeding-wise) if the TDS goes over 250ppm....

Bill
 

Tom Barr

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Re: Using a TDS meter to gauge EI

Some folks suggested about 30-40ppm for TDS for EI, I added a total of 100ppm, but that's for heavily fed fish tanks.

I think 100 is about right.

This is not killis which need soft clean water, but rather just a range for EI water change times.

Regards,
Tom Barr
 

Tom Barr

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Re: Using a TDS meter to gauge EI

Pretty much, but it needs tested on more tanks.
This is for one heavy loaded tank with Discus.

This notion goes well with maximum loading rates/heavy fish feeding.

There is a fair amount of TDS from fish waste and plant decay.
In maximum cases, about 75%

So if we assume the rest is from eI, or roughly 25%, this corresponds to a workable range..............

So we can focus on the range of 20-30-100ppm increases over a wide range of fish loads.

Some tanks may be more resistant and be able to handle more TDS if those fractions come from inorganic sources.

But we should error on the conservative side.

100ppm seems good, that's a lot of ferts: eg KNO3, KH2PO4, traces, GH additions, and some room for fish loading also.

I think adding say a relative % of K+, NO3, SO4, Ca, Mg, PO4, Fe/Mn/Zn/Cu/B/Mo etc of the TDS's will build up to to a max level of a grand total of 100ppm extra TDS's.

I mean, 20ppm of NO3, 5 ppm of PO4, 20ppm K+, and the rest are added in small amounts, less than 5ppm for traces, so the SO4/Ca/Mg can have a 20ppm or so increase, that leaves about 30ppm for fish waste on average of build up.

This is not the starting ppm for say GH, or NO3, K+ etc, those are set prior to this build up over time.

So you start at 15ppm of NO3, 20ppm of K+, 2ppm PO4, 100ppm of GH, 0.5ppm of traces etc.........

If the NO3 hits 35, 40ppm K+, and so on............then you need to do the water change.

If you can dose and keep that TDS down and stable, then you can leave it if things look decent.

This will not tell you what to dose or not, it will only tell you the total.
So you can use a ratio and see how well that works.

Note, this is based off one or two tanks.
It might be tougher to generalize.

But it will tell you easily if there is build up.
The amount may be used to gauge when a water change is needed along with plant health.


Regards,
Tom Barr
 

matpat

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Mar 29, 2005
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Re: Using a TDS meter to gauge EI

I have been using the TDS method of timing my water changes since early May of this year. I have a trio of Cobalt Blue Discus and two trios of Apistogramma borelli in my 75g tank.

My tap water has a TDS of around 220-230ppm. I change the water when my TDS climbs to the 300-350ppm range. It is currently 360 and due a water change. I may be holding off on this water change since I have one female borelli with fry and another female with eggs in the tank.

I dose about 1.5-2ppm of KNO3 per day and 0.3-0.6ppm of PO4 every other day with 10-15 ml of CSM+B on days opposite the PO4 dosing. With this modified EI dosing, I have been able to extend my wc's as far as 8 weeks (yes, with the Discus in the tank). However, at the 8 week point my TDS rose to 400ppm. That is the max I have let it go before a water change. Not sure if this was the limit but since this is the tank in my living room I don't usually push it too far. I may just push it this time since I have fry in the tank :D
 

Laith

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Jan 24, 2005
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Re: Using a TDS meter to gauge EI

Ok, help me out here.

What is the difference between a Conductivity meter that measures in us/cm and a TDS meter that measures in ppm?

Are they the same thing and you just convert us/cm into ppm?
 

matpat

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Mar 29, 2005
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Re: Using a TDS meter to gauge EI

They are pretty much the same thing. I think all TDS meters actually measure the conductivity of the water and either convert it automatically or require a manual conversion by the user. With my Hanna 98129, the TDS is factory set to be half of the conductivity (i.e. 400us ~ 200ppm), though it is changeable. Not sure why one would want to change it though :)