Deficiency or bug problem?

tough to be certain, but at 400tds, you can probably feed more... this assumes there isn't some crazy out-of-ratio mix of nutes... that'd be tough to be true given context. go up near 650-750 ppm. or 1.3-1.5EC on US scale (typical US/NA sold product.. if in europe, the conversion is different.. use google and a little algebra) you can see a light mix in most of my diaries. each week i post a screenshot of my ppm breakdown per nutrient needed. it is not always updated to current mix, but a ballpark idea is all it can communicate anyway. many factors will potentially cause different needs. my tap is very hard water, for example. yours may not be. that'll affect Mg/Ca ppms a bit. a weaker light may need a little less, vpd differences, etc etc manic botanix has an online nutrient ppm calculator (google) ... plaay with your concentration of each component to get something near my ratios and total ppm. doesn't have to be perfect. you'll still be observing and reacting, but should be close to starat and allow you to be patient as you adjust. in coco you fertilize every single irrigation. feed 650-750ppm wth 10% runoff each time religiously, and if it is a good mix you will very rarely run into problems. the runoff avoids buildup of salts effectively. how frequently you do so depends on weight loss of pot... a wet dry cycle is healthier and more easily avoids potential problems, but frequent irrigations can increase yields... i'd go simple at first and get a solid routine down before trying fancy stuff like frequent irrigations. easy next step if you do. 30% perlite or similar in coco.. if you switch to sphagnum peat moss (also "soilless") you want a 50/50 mix cause peat holds a greater volume of water. this ensures your roots are as healthy as can be.