Which is more important? RO or DI?

[AZDesertRat]

There is no such thing as getting too much in a RO/DI. You either get one thats reef quality or one that is not.
When you get a reef quality system you get 0 TDS not 0-20 TDS. The advantage of buying a better system is lower overall cost of ownership due to reduced maintenance requirements and filter/DI changes. Yes you may pay a little more upfront but it is returned many times over the life of the system.

80 TDS out of the tap is very good but still not reef quality and it would require a RO/DI to get that to 0 TDS. You could do it with DI alone but the cost of resin replacements or recharging would soon exceed the cost of the reef quality RO/DI in the beginning.

[binford4000]

There is no such thing as getting too much in a RO/DI. You either get one thats reef quality or one that is not.
When you get a reef quality system you get 0 TDS not 0-20 TDS. The advantage of buying a better system is lower overall cost of ownership due to reduced maintenance requirements and filter/DI changes. Yes you may pay a little more upfront but it is returned many times over the life of the system.

80 TDS out of the tap is very good but still not reef quality and it would require a RO/DI to get that to 0 TDS. You could do it with DI alone but the cost of resin replacements or recharging would soon exceed the cost of the reef quality RO/DI in the beginning.

20 tds is still reef quality water,really it's a 29 gal tank she has and it will take years for a filter and di change even on a cheap unit.Matching the unit to the systems needs is only practicle.If she has 80 tds out of the tap she can run it thru just about any filter system and get quality water.