Same problems every crop mid-flower

[Sascwatch]

Currently on my 5th crop of Master Kush that I got from a friend, the strain is of unknown genetics. Plants are in PROMIX hp in 5 gallon pots. Currently in week 4 of 12/12 under a 1000w HPS. Temps range from 24c lights on to about 17c lights off. Humidity is 40-55%.

The problems begin about 2 weeks into flowering and look like early stages of nute burn, dark leaves, purple stems and minor tip burn. I though this time I caught it in time with a good flush and a couple sprayings of just tap water. But that's not the case unfortunately.

Now into week 4 of 12/12 and the plants are showing multiple deficiencies. Magnesium and potassium are the 2 that stand out the most. Plants are showing burnt edges and tips along with yellowing of the leaves with green veins. Some also show dead spots on the leaves. Any affected leaf ends up getting eaten by the plant, dried up and is removed.

I've been feeding about 30% strength bloom ferts every other watering. They have been fed twice since the flush and continue to worsen. I figure I have been under feeding them as I measured the ppm and its under 400. They are due for their next feeding and I think I need to increase the nute strength. Going about 4 days between waterings. Also using cal mag at 50% strength each feed.

One thing I've been seeing this crop is a TON of spring tails in my soil. I have confirmed with a magnifying glass that they are spring tails. I've also noticed a few fungus gnats, but have them under control with fly strips. Is it possible for the springtails to cause a problem in massive numbers? When I water there are literally thousands of them floating on the water.

Will try and post some pics when I'm at the site next. Thanks in advance.

 

[Weaselcracker]

The feeding does sound low.
What ph are you running them at and is the meter calibrated and working properly?
What your watering cycle- how many days between waterings, what size pots, and are you letting them dry nicely between waterings?

 

[Sascwatch]

I forgot to mention that new growth looks good so far and they are packing on the buds. At this point most of the fan leaves are affected while any smaller sugar leaves are in awesome shape.

Using a bluelabs ph meter and a Hannah pen to measure the ppm. Both have been calibrated every 2 weeks. Feelings are done at 5.8 and waterings are at 6.0.

Pots are super dry between waterings, about every 4 days.

Could what I think are signs of nute burn actually be deficiencies? And flushing them causes them to go hungry?

Will also add that the 6th generation is currently at week 2 of flowering and started showing deficiencies so we upped the feed to 600ppm using a PK booster. They seem to have recovered a bit since the last feed.

 

[Weaselcracker]

Your watering and ph sounds great.
With the pure sativas I grow I max out at about 750 ppm. With the indicas- about 1100. I am a low nute feeder compared to most. Yours is way low though. Kind of almost nice to see somebody underfeeding, instead overfeeding like most people do. Yeah- they can definitely show big problems with underfeeding. In my experience- if a flush made it worse, and ph and watering checks out ok, then I would look at the feeding level.
It's normal with most deficiencies for the older growth to take the hit first. The damaged ones won't heal, so keep an eye on the leaves that are next in line for showing problems.

 

[Sascwatch]

Awesome, thanks for the help. I'll bump the ppms up and see what happens. Any ideas on the springtails? Everything I read says they do no harm, but with the numbers I see I would expect them to cause a problem.

 

[jare]

Fungus gnat's larvae eat roots, causing them to rot so that your plants have problems taking nutrients in. Controlling the flies with sticky paper strips isn't enough, get some Nematodes into the medium to eat the larvae. I don't know what ring tails are, but I'd try to get rid of them too.

Also stop watering, gnats live in the top few inches of soil and love nice damp conditions. Covering the soil with something they can't get through would help, and maybe do some gentle foliar feeding every few days.

 

[Sascwatch]

I've caught about a dozen fungus gnats in 2 weeks now, but it would make sense that there is more than it looks like. Springtails eat dead and decaying matter. Soil is plenty dry between waterings, and I haven't seen a gnat larvae yet. I recently put some diatomaceous earth ontop of the soil covering it completely, should take care of any insect trying to enter via the surface.

Once my plants are done and harvested, I am going to do a very thurough inspection of the soil and roots to see what my problem is.

Thanks for the help.