# Reverse Osmosis Water - Relation to TDS??



## REDSTEVEO (29 Apr 2015)

Hello All,

Anyone who has read my journal 'The Full Monty' the planted Discus tank lately will know that the Easter Bunny brought me a TMC V2 Pure 100 Advanced Reverse Osmosis system. I have not used an RO filter for years, so far I have been using a HMA filter changing around 150 litres per week. On average the tank water has always been around 250ppm and only dropping slightly after a water change using the HMA filter.

I have some observations based on recent water changes using the new RO filter.


My tap water in the house comes out at 94ppm
After passing through the HMA filter it comes out 116ppm (strange)

The previously recorded TDS in my tank before using RO water was 290 to 320ppm
Yesterday the reading in the tank was 250ppm
After changing 100 litres and adding 100 litres of pure non re-mineralised RO water the TDS was 150ppm, so a drop of 100ppm.

This morning the TDS was reading 149ppm
Today after adding another 100 litres of non re-mineralised RO water the reading is now 125ppm
According to that the difference is only 24ppm after adding the second 100 litres.
No additives, adjusters or ferts have been added during this experiment
So here is the point. According to the fancy in built meter on the RO system the water is going in at 155ppm and coming out at 5ppm which means it is removing 150ppm. I am adding this to the tank straight from the filter. Why then after adding the first 100 litres was there a drop of 100 TDS but today only a drop of 24ppm?

Also if you remove 100 litres of water which is at 125ppm and add 100 litres of water which is only at 5ppm why is the drop in TDS not more than the expected amount of approximately 100ppm?

Confused? So am I.

Cheers,

Steve.


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## kirk (29 Apr 2015)

Hello, I'm no scientist, but the filter when turned back on will  alter your reading also I have found it changes during the day with the co2. Also plant waste substrate. Will alter it slightly.
Ada substrate also alters things.

Sounds like it's stabilising around 150,  adding ferts wi  change it quite a bit, I stopped ei completely on our shrimp tank infact i don't use any ferts ( in the shrimp tank)mainly because Ive found it increases it to much.
Now they are breeding like mad.  but the plant look terrible


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## REDSTEVEO (29 Apr 2015)

Cheers Kirk, I suppose we can't have it always, one or the other no matter how hard we try!

Steve.


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## Andy Thurston (29 Apr 2015)

now I'm confused... tds from my tap is between 60-80. I do 1 50% water change weekly and dose full EI. after the water change my tds is about 160-180, just before water change its about 240-250


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## kirk (29 Apr 2015)

Big clown said:


> now I'm confused... tds from my tap is between 60-80. I do 1 50% water change weekly and dose full EI. after the water change my tds is about 160-180, just before water change its about 240-250


   well I'm running for the hills now mate before clever people who could sit still in maths and science and not just spent the lessons staring out of the window,read any of my basics.


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## tam (29 Apr 2015)

How many litres is the tank? I'm guessing 100l is about 40% - which would give you a drop from 250 to 150.

Another 100l should have given you about 90 - not sure why you got 125 instead - either you read something wrong, something upped it or you changed less water - did you check the second batch of RO was still 5ppm?

The drop won't stay the same because the you have to calculate the percentages between the new and old TDS. It might help to think of it as adding 100l of 0ppm water added to a tank with 100ppm water won't mean you get 0 - you'll get in between depending on what the % you change is. This online tool will work it out for you: http://www.theaquatools.com/water-changes-calculator just read 'dirt' to mean TDS.

If you've got fish in there be careful about dropping so dramatically!


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## tam (29 Apr 2015)

Big clown said:


> now I'm confused... tds from my tap is between 60-80. I do 1 50% water change weekly and dose full EI. after the water change my tds is about 160-180, just before water change its about 240-250



So just after water change you've got 50% of TDS 250 water and 50% of TDS 80 water so you'll end up half way between -TDS165. I don't know how much an EI dose adds, you'd have to check before and after adding (give it a bit of time to circulate).


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## REDSTEVEO (29 Apr 2015)

tam said:


> How many litres is the tank? I'm guessing 100l is about 40% - which would give you a drop from 250 to 150.
> 
> Another 100l should have given you about 90 - not sure why you got 125 instead - either you read something wrong, something upped it or you changed less water - did you check the second batch of RO was still 5ppm?
> 
> ...



Cheers Tam,

The tank is an Eheim Incpiria 400 litre tank, but with all the rock and substrate there is probably only 300 litres of water in it. If you have got a tank with 100 litres in it and the TDS is say 150ppm, if you emptied the whole tank and added RO water at 5ppm million, wouldn't that mean that the new TDS reading should read 5ppm?

Steve.


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## REDSTEVEO (29 Apr 2015)

kirk said:


> well I'm running for the hills now mate before clever people who could sit still in maths and science and not just spent the lessons staring out of the window,read any of my basics.



Ha ha ha hysterical, that was me too.


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## Andy Thurston (29 Apr 2015)

kirk said:


> well I'm running for the hills now mate before clever people who could sit still in maths and science and not just spent the lessons staring out of the window,read any of my basics.


lol
perhaps steve's tank is heavily stocked, discus are big eaters and need feeding loads to reach their full potential. also perhaps the built in tds meter is pants.
 steve if your changing 1\3 of the water then you can expect it to be roughly 2\3 of what you started with ie. if starting tds is 150 then you should expect around 100 after the change.
I would use the same meter to check the ro water and the tank water


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## Andy Thurston (29 Apr 2015)

tam said:


> So just after water change you've got 50% of TDS 250 water and 50% of TDS 80 water so you'll end up half way between -TDS165. I don't know how much an EI dose adds, you'd have to check before and after adding (give it a bit of time to circulate).


that confirms that my tank/meter and doing their thing correctly. I'm more confused with steve's numbers because they don't really add up and I know steve doesn't dose ei after having some problems, so the tds must come from fish and feeding rather than ferts.


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## tam (29 Apr 2015)

I agree Steve's don't add up, both measurements seem a bit off, because a drop from 250 to 150 when changing 100l implies a 40% change which should mean you had about 225l total volume which seems a bit low. A drop from 150 to 125 implies a 20% ish change which gives a 500l volume. Neither is right so something a bit off with your measurements.

Did you check the new water in the bucket before adding with your meter of just go off the readout? 

Changing all the water should give you the same TDS as whatever water you put it, as you haven't added/mixed anything to the water - just moved it from one container to the other - bucket to tank. However, in practice it's likely it wouldn't stay at 5ppm as your substrate/rocks may up it and even traces of the old water could do. Just using a buckets that's had water in before can up it slightly - particularly if that water evaporated previously. It should be much much closer to 5ppm though (which is too low for fish btw).


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## REDSTEVEO (30 Apr 2015)

Thanks Tam, Big clown, tomorrow I will compare the TDS reading from the meter on the RO unit to a measurement with a seperate TDS meter and see if there is any difference. The water has been going in straight from the RO unit, so no buckets involved.

Incidentally do you know if the lower TDS in the water has any bearing on any form of algae? Also what is considered to be the ideal TDS for discus?

Cheers,

Steve.


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## tam (30 Apr 2015)

Not sure what your previous filter stripped out, but tap water usually has nitrates and the calcium/magnesium etc. that make up hardness, which plants need some off and RO removes -so striping it right back might effect algae/plants. I've had algae grow in RO storage containers. 

I don't know much about discus but I've seen people mention ideal TDS depends a bit where they come from - having no gh/kh will make your ph more prone to swinging too so I think some people keep it up a bit to give stability. Usually with RO you'd use a buffer - either powder or by mixing in some tap to bring you up slightly. Easiest thing is to mix up water until it's the gh/kh you want and then measure the TDS and you'll know to mix to that TDS next time.

Keep in mind the TDS of the old water in your tank might be made up of various things, so TDS 200 mixed up with buffer powder might have a gh 7 kh 4 (example only it depends on the buffer) but a tank with a TDS of 200 might have much softerwater water as part of the TDS is from ferts or fish food rather than the stuff that makes up gh/kh. So just pumping in a lot of RO and no gh/kh might end up with much softer water than you'd expect.


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## ian_m (30 Apr 2015)

Also remember a standard cheap RO unit does not safely remove chloramine from incoming water, in fact can make it worse leaving ammonia (and chlorine to damage the membrane) in the outgoing RO water which will give a correspondingly high TDS reading and as someone above pointed out will allow algae to grow in supposedly pure RO water. You should always test your RO water for ammonia (the most common) or high TDS as a symptom of chloramine being used in incoming water (or add dechlorinator).

You need a Chlor+ carbon pre-filter to remove chloramine and preferably a DI resin on output and all filters with in date to ensure RO is really RO.


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## Rahms (30 Apr 2015)

REDSTEVEO said:


> Thanks Tam, Big clown, tomorrow I will compare the TDS reading from the meter on the RO unit to a measurement with a seperate TDS meter and see if there is any difference. The water has been going in straight from the RO unit, so no buckets involved.



Are you continually changing throughout the week, or are you removing 100L first, and then adding 100L RO?


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## REDSTEVEO (30 Apr 2015)

Removing 100 litres and then letting the tank fill back up direct from the RO unit, this week I have changed three hundred litres and so far no negative effects, no swing in PH etc, just need to check the KH and GH today in case my Crypts start melting.

Steve.


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## Rahms (30 Apr 2015)

Fair enough, was just trying to work out why the numbers could be off. But if you're doing it like that then I'm stumped.  Dodgy readings I guess


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## ian_m (30 Apr 2015)

Rahms said:


> Dodgy readings I guess


Please measure the ammonia of your RO, could be due to chloramine in your water supply.


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## REDSTEVEO (30 Apr 2015)

Just measured the TDS coming out of my V2 Pure 100 Advanced RO filter - water going in is at 152 TDS and coming out at 7 TDS going by th ereading on the built in TDS meter, using my hand held TDS meter the TDS reads 8 TDS so not much difference between the readings which tells me the one on the RO unit is pretty much accurate.

Changed another 100 litres today. The tank water readings now are:

TDS 114
PH 6.5
KH 2 DKH
GH 4 DGH
Temp 29 degrees

Prior to the water changes using RO water the readings were:

TDS 250
PH 6.5
KH 6 DKH
GH 12 DGH
Temp 29 degrees

Fish seem happy, water looks crystal clear.

So drop of 4 in KH and a drop of 8 in GH, and a total reduction / change in TDS of 136 TDS.

Possibly time now to add some SERA minerals before my crypts crash!

Cheers,

Steve.


ian_m said:


> Please measure the ammonia of your RO, could be due to chloramine in your water supply.



Ian, if I have got zero ammonia in my tap water going in to the RO unit why would the water coming out contain ammonia?

Cheers,

Steve.


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## ian_m (30 Apr 2015)

REDSTEVEO said:


> Ian, if I have got zero ammonia in my tap water going in to the RO unit why would the water coming out contain ammonia?


Because if your water company is using chloramine instead of chlorine and you have crap pre-carbon filtering (or worn out pre-carbon) the pre-carbon will break the chloramine down to chlorine and ammonia. The chlorine will kill your membrane and pass through and the ammonia will just pass through into the RO water. The marine big boys generally test their RO for presence of chlorine & ammonia or just add something like Amquel+ which will take them out. This is where the ammonia (and associated tds) comes from.

Using a Chlor+ pre-carbon filter, to remove the chloramine and an output DI resin will prevent this.


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## Rahms (30 Apr 2015)

The numbers really don't seem right. If you've added 100L@8ppm to 200L@250ppm, you should end up with 300L@~169ppm.  Obviously you don't have _precisely_ 300L but still.  The absolute most the concentration can drop is by 1/3rd, if you happened to have 0ppm RO. The numbers you're providing say that you're taking out more than 50% of the TDS by removing 33% of the water. It doesn't add up. For this to be true, your waste water would have to have a higher concentration than the tank it is removed from...

Are you taking the TDS readings directly after doing your water change? The only thing I can think of is that its not fully mixed when you're testing it. That or the TDS meter is fudging results at higher concentrations

edit: any chance you've hugely underestimated the volume of your hardscape?

And the TDS meter can be further tested vs your RO one I suppose- compare tap values and tank values if you can!


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## GHNelson (30 Apr 2015)

Hi
Just a point!
If your adding Pure RO WATER!
You need to remember that if you switch off external canister filters when doing testing  there will be non- accurate readings when the filter is  turned back on........because there is stagnate water in the filter chambers!
hoggie


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## REDSTEVEO (1 May 2015)

No mate, I leave the filters running the whole time, 100 litres out and then just leave the hose from the RO unit in the tank to replace the water, takes ages but this way I don't have to pfaff about carrying buckets and containers and worrying about temperature changes etc.

After all this, I get water out of the tap at about 125 TDS, but in my tank I could never get it below 250 and always thought that was too high, so i thought I would try and bring it down. Today after the third 100 litre change the TDS was 114, but I measured it again after re-mineralising the water and its back up to 220 TDS, so was there any point in using RO water for the water changes if the TDS goes back up anyway after remineralisng the water?

Cheers,

Steve.


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## tam (1 May 2015)

Remineralising puts back in stuff taken out by RO, how high the TDS is depends how much stuff you put back in. If that TDS is too high for you then put less mineralising powder in. It depends on the brand how much they up the TDS. 

If your tap water is only 125 TDS that's pretty low anyway. Using tap with TDS 125 or RO remineralised to 125 will give you the same result. If your tap is 125 but your tank runs at 250 (I'm presuming you do pretty regular changes) then something in your tank is raising the TDS - ferts, rocks, substrate, food. You'd expect a tank to be slightly up but not double unless you're water changing very infrequently or adding a lot of ferts.


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## REDSTEVEO (1 May 2015)

Cheers Tam, this all makes perfect sense. One thing I noticed was that the colours of the discus seemed more vibrant after the water changes with RO water and a lowering of the TDS.

Steve


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