My friend is following the BioBizz feeding schedul...

any acid is fine - if pH is drifting it isn't because the acid you use is not stable.. it means the solution is not buffered properly to start. if it is a soilless context, this is a major fuck up of the manufacturer of the fertilizer. if it's soil-use fertilizer, i don't know, i guess it's just typical of soil fertilizers, lol, probably "organic" too, bwahah. Any acid is fine. Acetic acid is a great option - cheap and available most places, plus it doesn't impact nurtient ratio balance like some acids and bases can. People confuse causality when it comes to pH drift issues. You can easialy mitigate the excess proton acceptors (bases) with some acid and have plenty of Mg and Ca floating around without an alkaline pH. It's done all the time and it is necessary for healthy growing. that symptom looks like a Cl deficiency, which would be very odd, so i'd assume pH in rootzone or nute-related lockout (see mulder's chart) is the cause here. Bronze coloration is odd. Trace elements are rarely an issue even if you see symptomsm of a trace element problem. Maybe somethign interfering with K? but, this isn't matching up well for that either. in the end not enough info, and not spending 30mins dooing the math on those nutes. if it's a soilless context compared ppms to the following, if this is a "soil" ignore this part... N 120-130 - at least 100+ in flower phase too. P 40-60 K 180+ Ca 100+ Mg 75ish S 100+ Some of these can vary due to what comes in your water out of the tap. That would impact ratio of what is needed above. The overall concentration is more related to lcoal VDP and rate your platn drinks. Higher rate of drinking requires a lower overall concentration but retain the same ratios. A lower vpd may need a higher concentration. The key here is it gets the same mass of building blocks per day to math new growth. So, may need some small adjustments to Ca, Mg, S, but the others should be very close. OVerall concentration may need an adjustment either direction, but this is a low starting point at around 1.3EC. These numbers are calculated from guarantee analaysis labels and not using some shitty TDS pen converting (aka guessing) from electrical conductivity measured. The fact there are 3 or 4 conversion factors depending on what equipment brand you bought tells you how inaccurate that conversion is. in any soilless or hydro contex, numbers WAY off from these will eventualyl cauase issues even if it takes 1-2 months to see them. Can other formulas work well? sure, but if 99% of plants don't respond well to it, this formula is better, lol. It is not "my" formula and you can find similar ratios and such across several brands like Southern AG, Jacks 321 hydro, athena (5x more expensive for no reason), masterblend and others... this is no accident as it is research based formula with sample sizes that a small garden could never compare to. trust it... it's 10x better than anecdotal nonsense.