[M FORBES LTD]

I have merlin and TDS coming out is 30ppm,  into 700ml resin bottle, it last for 200ltrs at 000,  then it creeps up to 002, for 1/2 hour, then 003 and so on every 20mins,  it use to last for 1000ltrs,   why is it happing HELP>

[leapstallbuildings]

Using the normal calculation of 500,000/30(PPM) = 16,667 litres per 25k bag you would expect around 450 litres from a 700ml resin container.  Hoever, I'm uncertain if this figure is based on until the TDS starts to climb or until the resin is totally exhausted and doing nothing.  If the latter then it may be about right.
I have a Merlin that is producing water at around 16/18 PPM (it climbed because I needed to restrict the waste).  I have two resin containers in series after the RO.  This allows me to hold fire on changing the first resin container until it is totally exhausted (the second one takes the TDS down to 000 if the first one starts to expire).  My first container takes a bit over half a bag of resin and lasts nearly 6 months.  It might save you a lot of messing about if you did something similar.  Bigger outlay but more convenient in the longer term.  If you were to use a similar sized resin container to mine and use a similar amount of water it should last about 3 months if you have a backup DI.

[[GQC] Tim]

200l sounds a little bit on the low side, but it could very well be that your tds of your tap water has changed due to works or heavy rainfall or the like. 1000l from a small 700ml DI canister is only possible with a very low tds post RO.

700ml are really terribly useless, buy two 10l DI canisters, and hook em up in series. That way, even if the first DI is exhausted, it still acts as a prefilter for the first like so :

RO (30ppm) ---> 1st DI (Resin part exhausted)(003ppm) ----> 2nd DI (With fresh resin)(000ppm) ---> tank or pole.

As you can see, the first DI still removes 28ppm, that's 28ppm that the second one doesn't have to remove. If only using one, you would have to change the resin after it creeps up. This way your resin lasts twice as long.