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I'm using cold water and letting it get room temperature. My warm water has water softener salt in it. Does this mean anything? It doesn't seem like I could put the salt in the aquarium. I don't know, I'm looking stuff up right now.

ALL tap water has problems. its just always different
its fine to use tap but you need a soften to add to your water ALWAYS before you add it to the tank.

NO just buy a water softener from the pet shop. they sell all kinds of things.

:3

we had to buy some because our saltwater to do refills was too hard. we added stuff to make it hard but added too much >_<

i also own water softener for my 55 gallon freshwater tank because its black water (acidic & soft)

depends on what brand and how big the bottle is
i buy the biggest one i could fine XD

"The ideal solution is to collect rain water and dilute it with tap water until the desired hardness is obtained. Unfortunately, this method requires various precautions and involves certain risks. The guttering and storage tank must be of non-metallic material. They must be as clean as possible, and cemented roofs must be avoided (essentially cement is powdered limestone). This activity cannot be carried out in regions where the atmosphere is highly polluted because the rain will contain all sorts of unsuitable elements. Water collected close to or downwind of, industrial areas may be polluted. Collect only during prolonged downpours, and wait a few minutes while the dust and any other rubbish is washed away. It is highly advised to filter or strain the collected water through filter wool to remove any detritus.

Boiling water will remove some, but not all, of the dissolved salts.

You can also pass the water through resins, which capture the mineral salts and leave it very soft. This method, which is known as ion exchange, requires a well regulated flow of water and the resins to be changed regularly (use only resins sold for aquarium use). This may affect the pH, and, as it exchanges calcium ions for (usually) sodium ions, the result may be soft but still mineral-rich (and unsuitable for fish from mineral-poor regions).

In recent years a technique called reverse osmosis has been made available to the hobbyist. This involves utilizing a unit to produce water which is chemically pure, hence perfect for aquarium use. This removes all minerals but it is wasteful – some 45.5 litres of tap water are needed to produce 4.5 litres of mineral-free water. It cannot be used alone because when devoid of all its salts, the water becomes very unstable. The pH can then fluctuate widely in a short space of time, becoming dangerous for the fish. Also, the process involved in the removal of minerals, removes free oxygen, so there is nothing to “breathe”. It must be aerated heavily before use, and never used “neat”. However, the greatest drawback of this process lies in its high cost.

Filtering water through peat can effectively reduce the hardness of the aquarium. Products such as sera super peat (sera biopeat granulate in ponds) or the addition of sera morena, which contain natural peat extracts, trace elements and humic acids, can help to lower levels for softer water species. Other sera products such as pH-minus will also help to reduce hardness, in conjunction with water changes.

Finally, it is also possible to use a very soft bottled mineral water, either for dilution or for the small tanks used to breed fish. This water needs to be vigorously aerated because it is void of oxygen."
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Complicated...

I just tested my warm tap water. The GH is 0 but the KH is still >240.

kh is carbonate hardness. that is a very important parameter in saltwater and that level would be too high for even that. you dont need rain water to get the correct hardness @_@ we add pre-made powders or liquids and ours turns out fine
but for our saltwater tank we do use an RO/DI unit because there are too many nutrients and contaminants in tap water for a reef. but that costs hundreds of dollars

my kh in my 55 gallon tank is like...0-1.6...on their scale anyway...highest is 2.9-3.6...you want it pretty low

and if the product doesnt say anything about hardness/softness on its label then it will not soften your water..i looked that stuff up and its not going to do it

i wouldnt listen to anyone at the pet shop for advice sweatdrop