Originally Posted by socalgirl531
Should I keep using the AmQuel? Or is this messing with the natural cycling of the tank?
And no, I don't have any live rock and wasn't planning on adding any.
No, you should not be adding AmQuel during a cycle.
I am curious about your long term plans. You have set up a 30 gallon saltwater aquarium and used a freshwater filtration method. This filter is designed to take Ammonia and Nitrite and turn them into Nitrate. In freshwater this a fabulous filter. However, Nitrates quickly become toxic in a saltwater aquarium, needing to be kept at levels below 40ppm for almost all fish, and below 20ppm for many. Corals and invertebrates need Nitrate readings under 5ppm or preferably zero.
Keeping levels under 80ppm is almost impossible using this type of filter. The hobby experimented with filtration methods for most of the 1980's and early 1990's. Systems using biological filtration, such as biowheels, undergravels, sponges, and bioballs, were found to have very minimal success.
It will be possible for you to have success with this type of filter, but it will require you to keep extremely sturdy fish and only 2 or 3 very small fish. I would limit the tank to Damsels and Clownfish only. Most other small fish require live rock to graze on, feeding on the microorganisms, copepods, and amphipods which live in the rock. Larger fish will be a burden on the Nitrate load. Even fish such as Dwarf Angels and Hawk Fish will generally not thrive in this type setup.
A properly set up marine aquarium uses a thick layer of aragonite sand, live rock, and a protein skimmer as the only filtration method. Some hobbyists, including myself, also choose to run a hang on filter with activated carbon. However, no form of biological filtration media be used.
For the record, large fish only systems may be set up using a "pre skim" technique, which draws all water into a very powerful protein skimmer, with the output into biomedia. This method works well for 220 gallon and larger systems keeping Trigger Fish, Puffers, large Angels, Groupers, etc.
However, very frequent large-scale water changes are required, which usually means 50% of the water on a monthly basis. Even then, such systems have much more success with a deep sand bed and significant volumes of live rock.