Drop checker is required to measure proper CO2 level. The pH controller is totally unnecessary, a simple solenoid would of been better. Setting you system at a certain pH means nothing in regards to proper CO2 levels. You could be under or over the ideal and IMO it feels like you are under pretty far. Turning up the CO2 would be a good idea, but it is risky till you have a drop checker. You are basically running blind right now. It is working ATM. It also worked for me for a while too, till I found out the hard way why you should never run your pressurized CO2 blind. That lesson was learned at the cost of over 100 shrimp. A CO2 Drop checker costs $10 off ebay so its just silly not to use one.
Have you thought maybe high tech is not for you? IDK how you plan to get by with biweekly water changes. You might be able to later in the game, but setting up and balancing the tank will go much quicker with weekly water changes of 50%. Your going to need tons of ferts w/ biweekly and its more likely they will become unbalanced. Also your nitrate is low, shoot for 20ppm at least. As far as ferts I stand by the dry EI ferts, which cost about $25 for a 2 year supply for 75 gallons. Those seachem ferts you want to use cost $10 a bottle and probably close to $20 for a months supply, you need to dose higher then recommend for most of those ferts. For dosing fertilizer you are going to need Nitrogen, Potassium, and phosphate(though be very sparing with phos), and also a trace fertilizer. You dose NPK one day and traces the next day then just repeat that. If you are doing that you should get good plant growth. If you plants grow weirdly they you have a nutrient deficiency, which can take some work to fix.
This is how I run my tanks, but mine are setup for maximum growth possible. I desire growth, where you look at the tank each day and you can see change. This also means weekly pruning is normally required, which is okay since I sell enough plants to cover costs of fish food, ferts, and CO2. I don't always have time to sell everything though, tossed over a pound of plants last week -_- I always run out of room for the plants and got to balance plant room with fish swimming space(that doesn't always work out though lol) This is the same tank that is in my sig if I go two weeks without trimming.