"erik" wrote in message ...
Why not use an anion bed followed by a cation bed (or vice versa)?
What problems would I be facing?
I thought it would be better to have seperate beds so that recharging
is easier.

It is better to have separated beds for recharging, of course.

But it is NOT better for the performance of water filtering process.
I am not an expert in this field but I have read in reliable sources
that cation and anion bed generate ionic imbalance affecting
the performance of each other. Simply said - when you have water
with NaCl dissolved and you remove cation you do not "remove"
it - you replace it with H+ ion. Doing this you increase acidity of
water and lowering performance of the following resin bed. Similar
effect you can observe when you "remove" anion Cl- you do not
remove it, you replace it with OH- ion. To minimalize effects, in big
water purification plants they install SEVERAL cation/anion
exchange stations in chains to create very clean water. In a smaller
scale, "mixed bed" resins are such anion/cation stations chains
in a one case: they just work better, more effective when mixed
than if separated and connected in a chain.

As a disclaimer I repeat I am not an expert and I wrote above
from my weakening memory ;-) so I might be wrong in details.
But mixed bed resin works much better than two separated
anion and cation beds connected in a chain - that is a fact.

A practical solution in our hobby would be to use 3 containers:
first two for separated anion and cation resins - these will
take the dirty water and not last long (but you can easily
recharge them) and thirds filled with mixed bed resin for
water polishing - this one will last much longer in such setup.
For very small scale, like my 30 gallon tank, one mixed bed
resin last for more than a year, so I do not consider it an issue
and I do not plan to recharge resins until I will get a bigger tank.