Discus and riverine cichlids in general require water conditions quite different from their rift lake cousins. These fish prefer neutral (and even slightly acidic) and soft water. There are several methods for softening your aquarium water. The following list contains five methods available for softening your water.
- Peat - it absorbs and sequesters calcium ions while releasing valuable
organics into the water (humic and tannic acids that will also lower the
pH). A very good compliment to RO water, but it won't work well if the
buffer is too high. Like carbon, quantity is the key... Both Hagen and Eheim
sell peat for their filters.
- R.O. Unit - the best option IMO - it produces pure water without salts.
Aquarium salt needs to be added to the tank water (which will provide the
necessary electrolytes without the hardness). A unit can sell for as much as
$400 (it's mostly the gpd rating that determines the price).
- Rain Water - only when the pollutions levels and the frequency of
the precipitations make it feasible (a modified plastic garbage can could
filter out dust and debris and provide usable water). I can't recommend this
method because even the most pristine environments are not so pristine
anymore.
- Selective ion exchange resins - basically the water softener pillows
that removes calcium/magnesium ions by adsorption (you shouldn't use the tap
water types). Some will also remove toxic metals. Strong acids are required
to recharge them - not very practical, in my opinion.
- Driftwood and Duckweed - not very effective - the wood acts a bit like
peat (adding valuable organics), while the Duckweed can use some carbonates
during photosynthesis.
I know Aqua Pharm and Kent both make pillows. The science behind them is
sound, but they won't be cheap or practical to use on large tanks. □
