Please help with possible toxicity

Ok so I’m growing in dwc. I’m noticing with plants at about week 6-7 of flower they lose their sweet smell and it turns to an almost toxic diesel/ammonia type smell that really isn’t very pleasing. This has happened on more than 1 occasion at same time late in flower. so I’m assuming it’s a nutrient overfed/underfed or I dont know but it definately doesn’t smell like the almost edible buds did 2 weeks ago. Has anyone else had this happen. The foul smell is so consistent it’s got to be a common problem but I could be wrong. It almost burns your nose I would assume it’s not very good for you. Anyone with the slightest bit of help is much appreciated.
Also I’m using gh maxi series dry nutrients plus additives. Nothing really changes nutrient wise except I do notice it’s when I drop nutrient ppm level from 700-900 back down to about 500ppm that’s when the bad smell starts. I try to taper nutrients off towards the end off cycle. Could this be the cause?

You run a dwc? When is the last time you did a full water flush?

How do the roots look? The smell can be from what is called root rot

Does the water circulate?

Deep water cultures can be bad if there’s no way to recirculate the water inside.

Pop those tanks and see if the smell is coming from the inside. If so it might be time to build a rdwc or a under current dwc

Yeah it’s a 4 pot undercurrent system. Water flow blocked up 1 pot for a couple of days from roots, nothing drastic and has been rectified. I seem to notice the odd smell when I drop the nutrient level to 500pm. I replaced the mix yesterday back to full strength 900ppm. This morning the beautiful grape smell is back! Can anyone explain what might be happening here?

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What’s water temp?

Pretty cold coming into winter. I run a chiller it rarely turns on this time of year. Water Temps 15-20 degrees

No clue then, any foul odor I could only assume would be root or water related.

As long as there is good ventilation for the plant to breathe.

A night cycle so it can release its built up oxygen.

Everything should be fine. Keep an eye on roots and water. Smell the reservoir if it smells funky give it a quick change

If plants smell healthier with higher ppm…it works.

Last month of flower, I run my ppm’s at 1000ppm+ finish very high ppm’s.

good luck