if I use bio balls and things of that nature in my filters with carbon is there anything else I can add to the tank to help with ammonia and nitrates?
Now your askin' the right questions!
I did have a typo on my last post - Bioballs convert Ammonia and Nitrite not Nitrate (didn't catch it sorry) they expel Nitrate. Large Volume w/c's controls Nitrate HOWEVER in larger volume SW aquariums this can be expensive like $50 or more a month in salt + a mixing pre heating tank where you match temp + salinity. For most of us this isn't fesible, for ornimental invert tanks it's a big no no as alot of their food lives in the water column. 50% w/c = 50% loss of food. Alotta ppl choose to change the bare minimum of 10% w/c's to keep H20 levels fresh and retain maximum buffering capacity.
So lets take this as 35-40 gal weekly W/C's of a 75 gal tank are not for you for one reason or another. One way previously stated is a granular or liquid compound specifically designed to trap nitrate - granular for obvious reasons is better. Next - remove it's source called TDS (total dissolved solids) can be done thru carbon reactors and/or protien skimmers along with weekly gravel vac. Another method is Flora like Cheato in a refrigium
which eats the TDS , Nitrogen,+ PO4. However the use of Live Rock as a biological filter rather than Bio-Media is more effective.
Ammonia + Nitrite converting bacterias live in/on things with normal to higher levels of 02 - Nitrate converting bacterias live in low flow low 02 level conditions like under deep sand beds or deep within' pourous material, they don't get 5-8x tankwater turn over rate that the others do from your pumps. So you need a large volume of Rocks and/or sand to house enuff to be somewhat effective esp. w/ min. W/C's. Approx. 1/3rd the total volume of the tank should be a biological filter - the more the better. Nitrate bacteria grows slow as in it can take years for an eco-complete
system aka a fully matured tank. So with min. w/c's most of us employ the other Nitrate removing stuff w/ LR.
Sumps can be very helpful w/ removing Nitrates - stand alone they do very little except add water volume lowering the PPM slightly. The sump gives you room to house things like Large Skimmers (bigger the better), Refrigiums, and Carbon Reactors as well as filter socks to remove larger solid particals.They also give you an option to add LR if you so choose for more room in the main tank or increased Bio-filtration.
Although none of this is nessassary for F/O tanks w/ large volume w/c 's - the above is how alot of us do it. A few things that can help with Nitrate build up - RO/DI water as Tapwater can contain 3-4 ppm of Nitrate and a high level of TDS - RO is Zero. A Testkit is invaluble when adding fish, go slow, add more when nitrates are very low allowing the LR, Skimmers, Refriums, + Reactors to keep up. But remember the most imporant thing is go slow - all this can be fornot if you overstock, overfeed, under maintence, and stock to quickly.