My tank has two light fixtures over a floating basking rock. One light has a UVB (i checked it is UVB not just UVA) and one from rona for heat. It has a submersable filter designed for a 40 gallon tank. The temp i keep with a heater at about 75 or lower. The basking rock is about 85. I have some live plants and i feed him about 7 reptomin pellets every other day and fresh veggies. He doesnt eat lettus kale or any leafy greens but he loves broccoli tomatoes cucumber and zuccini. The water i keep a little deeper then normal at abotu 5 inches from the top. It has a fake hollow log large enough so he can stand on it and be at the surface opposite the basking rock in case he gets tired. I have never checked the chemical levels so i wouldnt know them. If i get on the honor role in june my perants are going to buy me a 100 gallon tank for him. if i dont get on the honor role i finaly get permission to buy it myself (i wanted to get it 6 months ago) it has no gravel.
I went on turtleforum a week after i rescued him from being neglected so i knew what to do. What i need to know is if i can get media from the tank and what it is exactly so i can get it out.
I do a 50% change every 2 weeks. The turtle is 5 inches and the shubunkin and pleco are all the same sise. The goldfish get eaten within a week (exept for Bear Grylls who has lasted 6 months and is 2 inches) and the ones that arent eaten by that time i catch with a net and hand feed him them about one a week.
he also has a piramided shell and some some scars.
Fantastic that you have a game plan for him. At 5 inches he should really be in a 40-50 gallon by now but if you can get a 100 gallon soon, that's great.
I would very, very strongly suggest you get a liquid test kit to measure the chemical pollutants in the tank. These are chemicals that are caused by animals' wee and poo as well as any uneaten food and can be very dangerous to both fish and other aquatic or amphiborous animals. The damage caused can take weeks or months to show - sometimes years - but it is often very bad when the animals do start showing signs. The chemicals you need to be testing for are ammonia, nitrite and nitrate.
I would also up the temperature to 78F with the heater. This needs to be done slowly but low temperatures can cause long term health problems for the turtle. The goldfish should not be kept at these temperatures so I would stongly suggest rehoming any that are not destined to be eaten. The 20 gallon would make a good temporary home for the shubunkin when you move the turtle but ultimately the shubunkin (if it is a single-tailed variety) will need a pond. Depending on the dimensions, even the 100 gallon might not be big enough as it will only be 380 litres or so and that generally means a 4 foot tank. The goldfish should reach 12 inches or more.
Did you mean a medusa plec? With the bristles on its nose? Assuming it doesn't get damaged by the turtle it will be OK for now but there is a good chance the turtle will hurt it as the turtle gets bigger.
Goldfish are also generally considered awful feeders due to potential for parasitic infestations and low nutritional content. They are better if you can isolate them for a few weeks before feeding and treat with a wormer, though. If fed straight from the shop, it's a disaster waiting to happen.
Anyway.
Yes, you can use some media. Obviously don't take all of it and without a decent set of water tests we can't really say whether your tank is actually cycled (although I suspect it is). If you take 1/4 of the media and replace with new, the tank shouldn't be adversely affected too much. The media needs to be kept wet at all times and must be "fed" within 24 hours (either with pure ammonia or with fish waste) to stop the bacteria dying. So basically, move from your tank to wherever it needs to go very fast and make sure it gets exposed to a fishless cycle (using an ammonia source) or a stocked tank ASAP.