#### REDSTEVEO

##### Member

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

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.