If your CO2 levels are not that high, and you don't want to do 50% water changes, you can easily cut the doses, in half for example. There isn't really a rigid number for that, since it depends on many things, like how densely planted, how much light, etc.
One thing you can do is to get a NO3 testkit and do some testing. Tap water, tank water, distilled water as reference, etc. Over the weeks you will get a very good handle on how much to dose without starving plants or turning things brackish.
Regarding water changes... A long hose does many magic things.
You can build an easy contraption to hang over your tank, connect the hose, let it drain to a certain level, then connect the hose to a faucet and refill.
Or go semi or fully automated. There's a link in my sig showing one of the many possibilities for that.