Right so a couple of weeks ago I took my water to get tested at Pets At Home (As one of my fish disappeared; I assumed he'd died and been eaten over night) and we discovered that all my levels in the water were perfectly fine except for the Nitrate levels which were off the scale.
In a bid to improve it, we agreed that I needed to do a gravel clean and a 25% water change. We agreed that I needed to treat the new water with tap water treatment and I was also sold something called Nitra-zorb to put into the filter and was advised to come back in a few days as the nitra zorb should have a fairly fast effect.
Anywho, I did as we agreed and I went back for another test and yet the Nitrate is still far too high! I couldn't believe it. They asked me if I had lost any more fish and I explained that I hadn't yet, so I asked them what to do now. They advised that I did another gravel clean and water change. They also advised me this time to use something called NutraFin to try to help with the filter and hopefully lower those Nitrate levels.
They then told me to come back a week later; but now 4 days on, I have lost another fish

and it's really upset me losing another one. I just don't understand why I can't get this water sorted and it's really stressful. I don't want to lose any more of my fish.
So now I'm at a stand still and I really don't know what to do.
I've been looking up Nitrate levels on google and things to try and get help but they pretty much state the same thing as this:
Keep the tank clean Waste ultimately produces nitrates. Cleaner tanks produce fewer nitrates in the first place.
I am keeping the tank clean regularly as you can see I have down to gravel cleans; cleaned the glass and done a water change in 1 week because of the problems I'm having.
Dont overfeed the fish Overfeeding is a significant contributor to excess nitrates and other undesirable wastes, such as phosphates.
My fish are being fed once a day; which I wouldn't have considered as over feeding but correct me if I'm wrong.
Water changes Performing regular water changes with water that has little or no nitrates will lower the overall nitrate level in the tank. RO/DI water is an excellent choice for keeping nitrate levels low.
The problem I am having here is I am doing regular water changes, but the water changes in this area have very very high nitrate levels D= so I don't know how to break them down!
Keep live plants Live plants utilize nitrates, and will help keep nitrates in check.
I also have live plants in the tank.
Use nitrogen removing filter media Instead of an expensive denitrator or special filter, use special media in the filter you have. Although they will not lower nitrates dramatically, if used together with other methods the net result will be beneficial.
I am currently using that Nitra-Zorb in the filter to help D=.
Please do your best to help me crack down this Nitrate.
Is it going to be a case that I need to do water changes litrally every day or every other day?
Stacey xxx