Looking for nutrient advice: I run RDWC (65L) and ...

J.R. Peters - Jacks Hydro Part A 5-12-26 Generic Caclium Nitrate Generic Magnesium Sulfate. I'd also recommend the No-N Part A 0-12-26. This allows you to drop N enough in flower without impacting the levels of other nutrients. If you buy in bulk, it's 4 cents per gallon. If this brand isn't offered in your region, look for something similar... A base fertilizer, calcium nitrate and magnesium sulfate. Megacrop, cropsalts, koshersalts, southern ag, jr peters, masterblend... Numerous brands out there do somethign similar .. even athena, but it's 4x more expensive for no reason under the athena brand. Floraflex, at one time, had somethign similar and it was even more price gouging, lol. Fertilizer ingredients, especially for a soilless/hydro context, are commodities. They don't come in different quality. Calcium nitrate is alwys calcium nitrate - there's no 'top shelf' calcium nitrate that costs more. They should be cheap. I have a 55-gallon reservoir. Never have pH problems.. e.g. jacks cal nitrate is ~70 dollars for 25lbs. Yara Liva 50lb bag is 35-40 dollars.... there is no benefit to spending 4x more on the jack's brand. Probably 1/5th to 1/10th of the cost of the popular marijuana brands with the fancy cartoon graphics on the labels like a sugary cereal trying to attrach children, lol - and even less expensive in some extreme cases. The other cheese-dick things greedy companies do is put the trace elements into one of the generic parts... to force you to pay the excess amount,but in those cases, better to buy the trace elements seperately and just mix in as another part. It may not be available in europe, but i bet there's a similar alternative.