Reverse Osmosis Water - Relation to TDS??

REDSTEVEO

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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.

  1. My tap water in the house comes out at 94ppm
  2. After passing through the HMA filter it comes out 116ppm (strange)
  3. The previously recorded TDS in my tank before using RO water was 290 to 320ppm
  4. Yesterday the reading in the tank was 250ppm
  5. After changing 100 litres and adding 100 litres of pure non re-mineralised RO water the TDS was 150ppm, so a drop of 100ppm.
  6. This morning the TDS was reading 149ppm
  7. Today after adding another 100 litres of non re-mineralised RO water the reading is now 125ppm
  8. According to that the difference is only 24ppm after adding the second 100 litres.
  9. 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.
 

kirk

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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:D
 
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Andy Thurston

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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
 

kirk

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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
:D 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.:D
 

tam

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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!
 

tam

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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).
 

REDSTEVEO

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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!
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.
 

Andy Thurston

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:D 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.:D
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
 

Andy Thurston

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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.
 

tam

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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).
 

REDSTEVEO

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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.
 

tam

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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.
 

ian_m

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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.
 

Rahms

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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?
 

REDSTEVEO

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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.
 

Rahms

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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
 

REDSTEVEO

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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.
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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