DI vs RO

[five]

Hi guys, may I ask for your advice.

What's the difference between DI and RO unit? In terms of the water quality output from them.

I read in another thread which mentioned 'RO alone will not remove chloramine, but deionization will.'

Does this means DI unit is sort of better than RO unit?

My intentioin is just to get some soft water for my apisto. Still trying out the best ways though.

Thanks!

 

[ed seeley]

Deionisation removes the unwanted chemicals from water by a resin that removes them from the water. It can, in theory, remove more from water than RO, and therefore produce purer water, but this will depend on the TDS (Total Dissolved SOlids) of the incoming water. Once exhausted, the DI units that remove TDS, need replacing (I don't think they can recharged). If you have water with a high TDS this could work out very expensive.

RO units work by forcing molecules across a partially permeable membrane. A a physical process they do not need replacing or recharging (well, they will eventually, as they will block over time but mine is 3 years old and going strong). But before water is forced across this membrane it has to have sediment (which will otherwise block the membrane), chlorine and, I believe, chloramine removed or it will damage the membrane. To do this all RO units have two 'pods' below the unit, the first has a 5 micron sediment filter (so this can't block the membrane) and an activated carbon filter (to remove heavy metals, chlorine and chloramine among others).
The water can then be forced into the membrane. About a fifth of the total volume flowing in will be forced across the membrane (to produce the pure, product water) leaving the larger molecules on the other side with the 'waste' water which will flow out of the membrane. Usually this waste water flows to waste, but it can be used where the quality of the water isn't as important as it has been filtered by carbon and a sediment filter and is better than ordinary tap water (it just has slightly elevated levels of the things removed from the other water). My waste water flows into my pond to give them a slow water top-up whenever the unit is used.
The product water is usually about 90%+ pure (depending on the RO unit's specifications) and the product water in some units is then treated by a DI unit to get the water almost 100% pure water (I don't bother with this for soft water dwarfs).

The problem with RO is that it is a slow process and can waste lots of water. Pure DI wastes no water, but the resin has to be replaced.

Personally I have an RO unit, without DI, that is connected to a 100Litre barrel with a shut-off valve so that once the barrel is full the unit shuts itself off. I then have a tap at the bottom to take water out when I need it into the 25l containers for water changes.

I change the prefilters every 6 months and they cost about £10 from the supplier where I got my unit from www.ro-man.com. I would definitely recommend an RO unit.

Sorry for the long reply, hope that answers your questions.

 

[five]

Hi Ed, thanks for your post. It's a comprehensive reply that answer my queries.

Cheers.