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TDS and how to get it to zero.

Total dissolved solids, or TDS as it is otherwise known can be the cause of many problems. One of the main problems that it can cause, is nuisance algae like i have had.

As you will know from following my blog, i have had major issues with Algae. The RO water with a TDS reading of 9 that was being used woud'nt have helped. So how do you overcome this?

Get yourself an in line TDS meter to establish your TDS reading. This meter measures the water before the Reverse Osmosis and pre filter stages. It is not unusual for tap water to have a reading of 300. These meters also indicate the reading after the reverse osmosis process. As expected this should be zero.

If like me you have a TDS reading above 0. You will be feeding the nuisance algae. Provided your TDS is quite low, for example around 10 you can be satisfied that your Membrane is in satisfactory working order.
If higher or your RO membrane is a few years old you might want to consider membrane replacement.

So your pre filters and membrane are all satisfactory you will find you still have TDS present The most likely cause will be that you don't use DI resin. This removes the last remaining dissolved solids from the water. To use DI resin you will need an additional pod for your RO unit. This is simply added to your Reverse osmosis unit after all stages, post RO membrane, and packed with DI resin. The result is zero TDS RO water. Simply refill with DI resin as soon as this reading rises.

My RO unit was a 4 stage unit  That i simply re-plumbed as follows.
  1. Tap water 
  2. pre filter
  3. carbon filter
  4. Ro membrane 
  5. DI resin
  6. RO TDS 0 water

A word on your shop purchased water. Please ensure this is checked and of cause as zero TDS. It is not uncommon for this have high readings if the shop doesn't regularly check.

Now provided you have 0 phosphates and  0 Tds water you should be algae free.


The Reefuge said…
Great read, thanks a lot!
Gareth said…
Your really welcome, this advice has helped me finally solve my algae problem.

This guide is the result of many hours and mixed views reading and seeking advice on reefing forums.
It is great advice. thanks

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