Hi and welcome to the forum
There's no such thing as a no maintenance or even low maintenance tank, especially if you are trying to grow garden plants (hair grass) underwater. This plant needs bright light, lots of aquarium plant fertiliser, and carbon dioxide (CO2) otherwise it struggles.
The lighting could do with some tweaking. Aquarium plants like equal parts blue and red light with a bit of green and top it up with white.
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You need to do water changes regularly even if the water tests are good. There are lots of things in water that we can't test for and they need to be removed as well.
You do water changes for a number of reasons.
1) to reduce nutrients like ammonia, nitrite & nitrate.
2) to dilute disease organisms in the water.
3) to keep the pH, KH and GH stable.
4) to dilute nitric acid produced by fish food and waste breaking down.
5) to dilute stress chemicals (pheromones/ allomones) released by the fish.
6) to dilute un-used plant fertiliser so you don't overdose the fish when you add more.
7) to remove fish waste and other rotting organic matter.
Fish live in a soup of microscopic organisms including bacteria, fungus, viruses, protozoans, worms, flukes and various other things that make your skin crawl. Doing a big water change and gravel cleaning the substrate on a regular basis will dilute these organisms and reduce their numbers in the water, thus making it a safer and healthier environment for the fish.
Imagine living in your house with no windows, doors, toilet, bathroom or anything. You eat and poop in the environment and have no clean air. Eventually you end up living in your own filth, which would probably be made worse by you throwing up due to the smell. You would get sick very quickly and probably die unless someone came to clean up regularly and open the place up to let in fresh air.
Fish live in their own waste. Their tank and filter is full of fish poop. The water they breath is filtered through fish poop. Cleaning filters, gravel and doing big regular water changes, removes a lot of this poop and harmful micro-organisms, and makes the environment cleaner and healthier for the fish.
Whilst you might not have ammonia, nitrite or nitrate problems, the number of micro-organisms in your tank will be growing exponentially due to lack of water changes and this will eventually cause problems to the fish and shrimp.
I recommend doing a 75% water change and gravel clean each week. If there aren't many fish in the tank or clean fresh water is limited, maybe do a 50% water change every 2 weeks. But water changes should be done regularly to help keep things clean and stop the pH dropping, because this will eventually affect the fish, shrimp and plants.
Even in the wild, rivers and lakes are getting water changed. They might not get any new water for half a year but they do get a massive influx of fresh water during the wet season and this washes away all the gunk that has built up. Keep in mind that rivers hold a lot more water than any fish tank.
