Nitrate issue - plz help

[jimmyjam923]

Im having a Nitrate issue lately and I cant seem to get it under control. I had neglected my tank for several months and 2 weeks ago it tested at 80 to 120ppm. So I started a vigorous regiment of 25 to 30% water changes and vacuuming every other day testing every time but it only seems to lower it at best to about 40 to 60 ppm. Yesterday i did a 50% water change and after testing finally felt i had the nitrate under control as it was reading about 5ppm. I tested it tonight and its back up to about 80ppm. Im at a loss for why the nitrates would continue to spike like that so i tested my tap water and have about 5ppm in that so clearly thats going to be the best it can get.
Here are my tank stats:
75g set up since 2013
Driftwood, rocks and fake plants
4 inch featherfin cat
(2) 2 1/2 inch plecos
3 inch convict
11 inch leporinus
API canister filter. Xp M
Aqueon 75 HOB

Ammonia 0
Nitrite. 0
Nitrate 80 ppm
Algae bloom is present

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[King Fisher]

Try not to vacuum to much of the substrate. For now, keep up 50% water changes and try to keep it in the 40ppm range. Try cleaning only the very top layer of substrate (light vacuum) once a week. Only do a deep gravel vac a few times a year. When you do this, only deep vac 1/3 of the tank. The next week do another 1/3 and so on until it's cleaned entirely.