First off, i handle husbandry of fish, and aquatic herps (reptiles and amphibians) at the North Carolina Museum of Natural Sciences (largest Science Museum in the Southeast US). The only way to truly eliminate any parasite issue is to quarantine your animals, and to perform skin scrapes, gill and fin clips, and examine fresh fecal material. Necropsy of freshly dead or dying fish is also a method. All the fish that the public buy in stores or online usually come from one of two main sources: farms in Florida and Asia, or are wild caught. All these fish carry a variety of pathogens. Usually some form of stress causes an outbreak. Fish properly housed, fed, and maintained will live for years with these pathogens with no outward effects seen. So remember unless they have been quarantined and treated accordingly, all fish carry some form of pathogen. Now to the temperature issue, fluctuations between 3-8 degrees are acceptable. Water temp. is not uniformly stable in any aquatic environment. I know what some of you are thinking out there, but even on reefs (the most stable ecosystems on the planet) temperature is not stable. Look at tidal pools, you think that they don't cook at low tide, and what about 30 to 50 ft down, its gonna be cooler. Even in river systems ie. the Amazon. When it rains at high elevations, and the water runs down stream, it cools the water drastically, also shaded areas are gonna be cooler than areas in direct light. With tropical fish as long as you are above the 73-75 degree range you should be ok. However there are some species that after years of captive breeding in ideal conditions, they cannot handle these fluctuations (ie. clown loaches). So the advice from others to try and stay on the warm end is excellent advice. Your filtration sounds like it is ok. Carbon is ok to use anytime, remember this is a closed system, and you cannot over-filter a closed system. Just one thing, carbon looses its effectiveness at around 21 days. I use the highest quality, laboratory grade, carbon you can buy at the museum and after 15 days it is replaced. On my most sensitive fish i use ion exchange resins. NO AMOUNT OF FILTRATION CAN SUBSTITUTE REGULAR PARTIAL WATER CHANGES. The advice given earlier on your sponges, and media is dead on, and i would follow it. As far as medicating fish, try to avoid medicating the actual tank. A vast majority of the medications for sale can adversely affect your bio filter, and why would you want to medicate the other fish that are not showing signs of infection. I would recommend isolating the infected fish, and 2 partial water changes daily to keep NH3, and NO2 levels in check and use 3/4 of the recommended doses. I have found after 23 years its better to under medicate rather than over. So get you a couple of quality sponge filters and tanks to keep on hand for quarantine, and medicating, you will be very glad that you did in the long run. Decaying plant material should not pose a problem unless there is an abundance of it, Plants are an excellent source of nutrient export, and cover for your fish. However remember this, plants use CO2 during the day, but O2 at night, so it is imperative that there is adequate surface tension agitation when using plants. Gas exchange only happens at the surface (bubbles in the water column provide current, the bursting of them at the surface is where the gas exchange occurs). All in all except for using your gravel vac more diligently to help eliminate your worms, everything elso sounds ok. I do question some of the fish you have put together, but in a tank that large that should not be an issue. Where exactly are you purchasing your fish from, and how does this store have their tanks set up???? Also what do you clean the outside of your tank with??? Do you or your wife use air freshener, or carpet powder in the room where the tank is??? Do you rinse your hands well before you perform maintenance??? Sorry that i am soo longwinded, i do tend to ramble. Answer these questions at the end, and i will have more for you to narrow this down.
