I have to say that I find setting ideal parameters fairly easy (with time and patience/practice).
Starting with pure RO/DI unit, add SMALL amount of GH booster of your choice( seachem is just fine), every 2 or 3 water changes, And a small amount of KH booster ( baking soda mixture as needed).
The chemistry is pretty straightforward, and pH management is not required if you do not have any substrate that leaches anything into the water. Photosynthesis/Co2 addition will swing this during change of photo cycle.
DI does has functionally neutral pH, but as it is Unbuffered, it will assumes hat is in the aquarium automatically.
For 240 gallons, I change about 30% of the water with direct feed DI overnight weekly, and end up with 2dGH, 2-3dKH, 6.8 pH and keep heaters set at 75F, utilizing room temp to end near 78f. The cold DI water is fed in at about 4-5 GPH with a 100 gallon per day unit, so the temperature of the aquarium is not affected at all over the course of 14-16 hours. The concentrate I run right into our lawn (grass loves it).
Our local water comes in at 6-8 dKH, 400-600 ppm hardness, 8.1-8.3 pH, and after DI you have 0-1 dGH, 0-1 dKH, and neutral pH with 100 micron, 50 micron, carbon, 98%RO membrane, then DI resin filters. This whole unit can be purchased for $200 or less, with filter replacement costing $100-125 every 7-9 months with heavy use.
With heavy plants, and EI dosing, all fertilizer levers (N/P/K) will be just right all week, get functionally reset at weeks end.