Left over residue in h2o salt mixed

[braincoral]

Anyone faced the above issue

Or because of salt expired?

[peacemaker]

Seems normal to me. I don't mix this in the tank but throw it away.

[vidextreme]

Actually, those are not 'residue' but precipated calcium carbonate. This happens when a calcium salt is exposed with carbon dioxide which is very common in our atmosphere.

Add of a bit of moisture and you get aragonite or calcite. Unfortunately, calcite is not so desireable to saltwater tank as they are not dissolvable, meaning... useless in tank. Aragonite

on the other hand act as good buffers for slow release of available calcium and/or available carbonate in tank, which means more stable pH upon presence of other helpful ions.

[vidextreme]

Oh btw, this is the main reason why mixing Kalkwasser(Calcium Hydroxide) mixture or any salt base Calcium Carbonate or pH buffers such as SeaChem Reef Builder needs much care to not to allow bubbles to mix these solutions. Presence of Carbon Dioxide in the solution will precipitate in Calcite or Aragonite depending on the availability of needed ions to form their crystaline structures. That's why also, it's not so advisable to use aeration or airstone in salt water preparation.

Hope this helps.