Umm having 0 nitrate.. isn't ehhhh exactly a great idea lol. You risk getting blue-green cyanobacteria algae. It may be a pain to eradicate, unless you know the right methods. Anyway, why is it that you don't want to do water changes? Very busy schedule?? I mean, well sure, purigen can definitely help.. but 0 nitrate isn't seriously recommended, in my opinion.. and plus, your plants will really suffer without some of it. I suggest you leave it at 5.0 to 10 ppm. Up the amount of fast growing plants you have in your tank to help eat up your high nitrate. If you could do a water change, you should just do it.. high organics build up over time, topping off the tank won't do the plants any good it'll add TDS, unless your plants extremely love metals, minerals, maybe it's okay to leave the TDS to increase, but meh it's just not good to have too much of it.. I highly recommend doing water changes to reduce the nitrate levels. Simple as that. By the way, how much do you feed your shrimps? You may possibly be overfeeding.
20 gallon - Sulawesi Golden rabbit snails/Japanese Trapdoor snails/RCS/Marbled crayfish tank
55 gallon - Rainbowfish Dutch scape low-tech planted tank
250 gallon - Community Tiger Oscar/Red hook silver dollar/Silver dollars/PB Jack Dempsey/Clown loaches/Tinfoil barb/Roseline sharks/Bala shark Monster fish tank