Water changes

[sphelps]

On more post regarding cost of dosing vs water change as that came up.

System size: 25 gallon
Demand: Low

Water change:
Decent salt brand - $70 / 150 gallons
Min requirement - 10% change per month
Cost: $ 1.17 per month

Dosing (rates are based on bottle instructions):
Trace Element - $20/500ml (5ml/week)
Mag - $10/500ml (5ml/week)
Potassium - $12/500ml (2.5ml/week)
Alk - $8/500ml (10ml/week)
Ca - $10/500ml (10ml/week)
Cost: $2.88 per month

So dosing will cost you more than twice as much and do less but it is easier.

[Arok3000]

That article also conclusively explains what Sphelps is discussing about removing unwanted build-up of contaminants.

Water Changes to Deplete Something: Sulfate from a Homemade Two-Part Additive

I have suggested that reef aquarists who cannot find high quality magnesium chloride could manage using inexpensive Epsom salts (magnesium sulfate heptahydrate). The unfortunate drawback of using Epsom salts is the accumulation of sulfate. The article goes on to show how water changes reduce the concentration of sulfate that is built up as a byproduct of splitting the magnesium sulfate heptahydrate.
Now I know that many aquarists are not using Epsom salts to dose their magnesium, but what other by-products are you unknowingly creating in your tank?

I use FCC grade anhydrous Calcium Chloride which is claimed to be 99.8% pure. Can you be completely sure that the other .2% of whatever you're dosing isn't building up contaminants? Food grade products are fine for human consumption, but in our digestive systems we don't typically build up toxic elements, they are excreted through wastes. In aquaria, these elements are built up in the water column, and without a means of removal, will continue to build up over a period of time. Although not immediately noticeable, even the tiniest amount of pollutants consistently added over a long enough period will eventually build up to toxic levels.

[reefwars]

I have to agree with sphelps 100% very we'll said