You might just drop the K altogether and use KNO3 (Potassium nitrate) instead. All those sword plants are nitrate hogs! They like lots of nitrate, so keep that around 10ppm. It's possible, when CO2 & light is available, for those plants to consume 5ppm per day or more! You should be able to get enough K from the KNO3 that you may not need to dose extra. KNO3 can easily be found at any garden center as Green Light "Tree Stump Remover." After trying that out for a couple of weeks, try dosing Phosphate. You can find this at any pharmacy as "Fleet Enema." I bet you're excited about buying that. Thank goodness for self-checkout nowadays
Sometimes you might be able to find a powdered form from a local nursery.