Reverse Osmosis Water - Relation to TDS??

[ian_m]

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.

 

[Rahms]

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!

 

[G H Nelson]

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

 

[REDSTEVEO]

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.

 

[tam]

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.

 

[REDSTEVEO]

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