This is by no means conclusive as it will depend on the type of carbon filter you use and I am not going to go into detail about each different type and just generalize on the subject. I suggest you check with your filter manufacturer first, and then treat your water appropriately.
Activated carbon filters remove some and reduce many volatile organic chemicals (VOCs), pesticides, and herbicides, as well as chlorine compounds, benzene, trihalomethane (THM), radon, solvents, and hundreds of other man-made chemicals found in bath water. faucet.
Some activated carbon filters are moderately effective at removing some, but not all, heavy metals. Additionally, the densely packed carbon block filters mechanically remove particles down to 0.5 microns, including Giardia and Cryptosporidium, turbidity and particulates.
While these higher quality activated carbon filters will remove some iron, manganese and hydrogen sulfide, a manganese iron and green sand reduction filter is generally preferred to remove these contaminants, as the effectiveness of the carbon filter against iron and manganese is generally short-lived if the contaminant concentration is high.
Carbon filters are generally NOT successful in removing dissolved inorganic contaminants or metals such as minerals/salts (contaminants that cause hardness or scale), antimony, arsenic, asbestos, barium, beryllium, cadmium, chromium, copper, fluoride, mercury, nickel, nitrates/nitrites, selenium, sulfate, thallium and certain radionuclides. Removing these contaminants requires a reverse osmosis water filter system or distiller, which is not recommended for an aquarium situation.
Many will claim all sorts of wonderful things that they can remove and one of the major misunderstandings is chlorine (Cl) removal or should I say chlorine reduction as it really can’t be completely removed as there is still chloramine left. The composition of chlorine is basically ammonia and chloramine.
Chloramine (monochloramine) a toxic substance (NH2Cl) created by the chemical reaction of the ammonia in your tank and sodium hypochlorite (chlorine bleach) that remains in your tap water, even if filtered through carbon filters. This reaction is more powerful in an alkaline situation, such as high pH tanks.
You can buy catalytic carbon filters specifically designed for chloramine removal, which would be better than carbon (charcoal) based filters. You can always use one of these to deliver water directly from your tap to your tank, but you’ll have serious nitrate and nitrite problems. The chlorine in the tap water would react with the ammonia in the water and produce chloramine and then the filter would remove the chloramine. Definitely NOT recommended.
Not to mention the elusive Nitrates and Nitrites, since they are very present in tap water, filtered or not. Just as effectively, if you are adding tap water to your aquarium, it should be treated before placing. To remove Chlorine you can boil the water. You can remove chloramine (NH2Cl) with sodium metabisulfite (Na2S2O5) a sterilizer. However, the use of sodium metabisulfite is NOT recommended, as it produces sulfur dioxide (SO2) when put into water. However, it is ideal for sterilizing bottles for home brews.
What options do you have?
Let it rest:
Chlorine will dissipate in 2-3 days sitting at room temperature. To speed up this “aging” process, you can add an aeration to the bucket or drum to agitate the water and help remove some of the nitrate at the same time.
Splash some chemical on it:
However, chemical dechlorinators work well if you use the basic sodium thiosulfate (Na2S2O3) then you will still be left with a lot of ammonia. e.g:
EPA guidelines set a maximum allowable chlorine level of 4 ppm. Most water supplies aim for 2-4 ppm chlorine. Keep in mind that 4 ppm chlorine is actually 5.8 ppm chloramine. (Chlorine is 69% of the chloramine molecule, ammonia is the other 31%). So with a possible 5.8 ppm chloramine, you have 4 ppm chlorine and 1.8 ppm ammonia.
There are dechlorinators (chemicals) that will also convert ammonia to ammonium (non-toxic NH4+), this is a conjugate acid of the ammonia base and just has an extra hydrogen ion. Ammonium in an aqueous solution (your tank) will dissolve to create ammonium hydroxide (NH4OH), which is another compound of ammonia and is still a weak acid. Since ammonium is considered a weak acid, it will lower your pH. The results of adding a product called “Seachem Prime” that will accomplish the above will differ at different pH levels, so be sure to check that first before application.
Marginal note – As far as dealing with ammonia, if you are experienced enough you can always add a bit of sulfuric acid to the calcium phosphate rock to create some phosphoric acid to mix with your ammonia thus turning it into ammonium phosphate which will feed its bacteria used in the bio-oxidation process to create carbon dioxide and water. But that’s a whole different conversation.
My apologies. I am straying. Yes, it is good to use a carbon filter (preferably GAC granulated activated carbon), although it is not recommended to totally rely on it, as the chlorine levels in your tap water will change quite frequently. Not to mention, some treatment plants are starting to use Chloramine instead of Chlorine, since it is more stable in comparison. So if that happens and you don’t know it, your crabs and fish will die.
Of course, use the carbon filter on tap water. However, I will recommend that you also let it sit for at least 24 hours at room temperature with an air stone. Just to be sure. I would even go as far as filtering the water and then adding something like “Seachem Prime” and then letting it sit aerated for 24 hours. But I’m pedantic when it comes to chemical reactions in water and the less I have to deal with the better.