Welcome to TFK!
Nitrates can be a problem especially in agricultural areas where surrounding land areas see a fair amount of organic and chemical fertilizers. I have very high nitrates in my well water the result of a 95 acre farmers field across the road. Although not as toxic as ammonia and nitrites, nitrates have long term negative effects on aquarium fish. High levels will inhibit immune systems, stunt growth and reduce life spans. Bear in mind that nitrates levels in fresh water in nature are so low they effectively can't be measured. As Romad points out, less than 20ppm or as low as possible in our aquariums. In fact, in SW, many corals can not survive in the presence of any nitrates. I had several fish losses before I realized a source water nitrate problem.
Unfortunately the usual recourse for nitrate removal from tank water is water changes which of course doesn't work when you have high nitrates in your tap/well water.
As you look to reduce existing tank nitrates Prime won't really help. It will detoxify ammonia, nitrites and nitrates for only 24-48 hours, but not remove them.
There are two products that may help in reducing the current tank nitrates. Hagen's Fluval Lab Series Nitrate Remover (FNR) and API's Nitra-Zorb. Both of these are ionic synthetic scavenger resins that adsorb nitrate. They are rechargeable several times with salt water. Note: API's Nitra-Zorb also removes ammonia and nitrite along with nitrate so may inhibit a cycling process.
To reduce tank generated nitrates, you can add living plants. Many standard aquarium light systems won't support rooted plants well, but nearly all will support floating plants that can reduce nitrates by processing ammonia (before they become nitrites and then nitrates) and nitrates directly.
Good tank/filter maintenance and proper feeding can go a long way in reducing nitrates by minimizing organic waste that decomposes producing nitrates. This may include periodic gravel vacuuming to remove decomposing waste.
Increased filtration/purification using activated carbon and products like Seachem Purigen can adsorb dissolved organic compounds preventing conversion to nitrates.
There are also products like Seachem Matrix bio-media that may help in reducing tank nitrates.
Finally is the issue of water to use for periodic water changes. Bottled water is about 1$/gallon. Perhaps you can haul water from another source?
You could install an RO (reverse osmosis) or RO/DI (reverse osmosis/de-ionized) system. However, RO systems require a constant water pressure of 50psi to force water through a filter membrane. Many home well systems would require a booster pump. RO water also uses approximately 4 gallons of waste water for every gallon of RO water produced (so additional plumbing may be required to handle waste water).
Instead, I purchased an API Tap Water filter to produce some de-ionized (DI) water. Unfortunately, cartridge use life is relative to water purity and my well water only yields about 50g of filtered water per filter ($25) cartridge. To offset this, I setup a spare 10g w/filter in my garage to filter tap/well water using the FNR product. I'm mixing DI and FNR filtered water 50/50 and have been doing a 10g weekly water change on my 60g tank for several weeks now.
As indicated, I'm using floating (anacharis) plants, good tank/filter maintenance as well as activated carbon and Purigen in the filter the reduce dissolved organics. I'm also developing a DIY bio-denitrate filter
(see DIY section in this forum).
I hope the above gives you some ideas on how to handle high nitrates in your source tap/well water.