Use a plasma water table additive like sterling cool
There are several different brands out there.
Really depends on your volume and type of material being cut also some people want to see clean fluid every time. so the range is daily to quarterly depending how you operate. I am closer to the later.
The Langmuir instructions say .75-1" from the metal being cut but I can not that reference right now.
keep your water level lower. move you torch over some metal at the end of the cut so the post air flow is not blow straight into the water.
I also have some strips of metal I use as a slash guard I manual place when cutting close to the edge of the table.
I move my electronic box from the factory location and mount to the wall near the table so I have nothing around water and hurt.
Welcome to the forum.
Tin gave you a great run down for all of your questions.
Here is a good comparison of products available including a brief description of just plain ole Borax.
The recipe most often quoted uses sodium nitrite but that product has been hard to come by due to its use in a number of suicides.
1/4 pound of sodium nitrite powder ($15/pound) “anti-rust additive” NOTE: nitrite NOT nitrate!
1 teaspoon of Physan 20 ($8/8oz bottle) “antibacterial/antifungal additive”
1 oz Ultramarine blue food-grade dye ($5/oz.) “color added so folks won’t drink out of it!”
Mix well, treats 75 gallons of water.