30-40% is not enough. if he is at 1 ppm that will only bring him to.6-.7 ppm still to hi dont worry about the % off water take as much out as you can and still have room for the fish to swim. fill it up and keep doing it till you are under .25 and you can just do a water change every 2 days or you can test your water and find out when you really need a water change. after a few months you will find out how often you need to do a wc it might be ones a day or once a month depending on how you feed and your stocking among other things.
I do 80-90% water changes. Think of it this way: 2ppm ammonia x 20% = 0.4ppm, after one water change. Some sensitive fish like clown loaches, don't like the large water changes, and you have to be careful to get the dechlor in there as soon as you start to refill, and make sure the temperature is close so you don't shock them.
The main limiting factors are what depth are your filter intakes (ideally, keep the filter running the entire time), and keeping enough water in there that the fish don't injure themselves flopping around in the shallow water. Also, make sure you have shatter resistant heaters or unplug them. After cracking probably a dozen heater tubes (anyone remember buying replacement "test tubes" to repair broken heaters?), I started paying more money and getting the shatterproof ones, and don't even worry about unplugging them.