Hi Steve,
Good old Tetra, simple instructions....for rocket scientists! OK DH and GH refer
to degrees of hardness, as you may know water is highly variable as to how
'hard' or 'soft' and how 'acidic' or 'alkaline' (the last 2 measured as pH)
Basically hardness refers to the amount of calcium present in the water, if your
local tap water comes from a source that filters through limestone it will be
hard and alkaline, through, say, peat and it will be soft and acidic. Most
tropical fish prefer water on the soft, acidic side (there are exceptions to
this, African Rift Cichlids for example).
Over time water will soften as the calcium content leaches out, you may see
white deposits on cover glasses or the tank lid, if however there is regular
partial water changes with fresh, hard water this will negate any natural
softening of the water, hence some people use water conditioners to help remove
(technically known as chellate) the hardness from the tap water. For fish
keepers who need a lot of soft water a Reverse Osmosis Unit (R.O.) is a
worthwhile investment. This device passes water through a membrane that removes
many potentially harmful elements including calcium carbonates. The resulting
water is then very soft and acidic (typically a pH of about 5.5!).
So short of investing a couple of hundred pounds in an RO unit what can you do?
There are a number of chemical additives that can help you, check them out at
your retailer, many Aquatic outlets sell RO water if you want to go that route,
distilled water is also usually quite soft, either buy it or boil lots of water
and let it stand (boiling removes calcium carbonates, look inside the average
kettle!. If your tap water is not very hard I find that if when doing a partial
water change you turn the tap on as hard as you can so that the water really
'boils' as it goes in the bucket (assuming you use one!) this can also help to
drive out the calcium (it's an old method but the one I've used for years).
Finally bottled water is generally fairly neutral to soft (but only use the
still type!!) but not all. If you write to your local Water Company they can
usually provide you with a chemical breakdown of your local water if it's of
interest to you.
Last but not least, are your fish suffering? Lots of fish can tolerate quite
hard water, many live-bearers for example, if they seem OK, perhaps cut down on
the frequency of the partial water changes for a while and re-test the water.
Sorry it's such a long reply, but water is a very complicated subject and the
above is just a very basic outline. As I've said many times, fish-keepers don't
really keep fish, they keep water! If the waters right, the fish will be. Hope
the above helps. Let me know how things turn out.

Steve

steve saunders <steve23eris@...> wrote:
Hi all,

Ok, so now im testing the water everday or so etc - im using the
Tetratest 5 in 1 - the instructions to which are about as clear as my
tank was three days ago! (or my mug I left in the shed for 6 weeks
but I digress)

My latest test seems to indicate that the GH level is too high.
Reading >16 degrees d (whatever that is)

Instructions advise me to 'add distilled water from a reverse osmosis
unit' !!!!!!

Can anyone explain to me what I need to do - please.

Thanks and all the best

steve saunders




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