Hmm as someone new to marine setups, i will still follow the use of test kits. I got a veryvery expensive and bad lesson of going with my gut feeling abt the parameters and using even a cheap multi test strip. It made my high grade crystal shrimp tank i had for a couple of years to crash, following the death and sell off of my shrimps and decomm of my 2ft tank(which became marine now). Test kits will help u eliminate possible causes of death, ie; ammonia burns/poisoning, too high/low dkh and such. It also helps when ur dosing nutrients in ur tank after water changes or weekly dosing. Example, change 20% of water will replace only 20% of nutrients from saltwater. If stocking of tank is on the extremes(very low/high), my own thought would be that depletion of nutrients will be different. Of course following manufacturer's instruction is best, but if i got, say, a low stock level, wouldn't weekly dosing accordingly be extra nutrients accumulating down the road?
Regarding the filter u wrote its not needed but ur using one, it can be added if needed, im using a hangon one which can have multiple uses like as a media chamber for chemical and bio medias, breaks water surface for circulation and increase oxygen levels, siphons out extra food, floating poo and stuff.
Which the above said, im in no way trying to put down anyone in anyway. this is written on neutral ground in accordance to my own experiences in freshwater tanks. no offence yea ppl out there!