Light green/yellowish leaves, all 4 plants

[umop apisdn]

Problem: The 4 plants are at 48 days now, about 1.5 weeks into flower and they are all very yellowish light green. They seem smaller (or stunted) than they should be. The leaves are all pretty small and pointing upwards towards the light. Some of the leaves have lighter bleach looking spots. Basically, yellowish, thin, pointing up, slow growth.

Medium/grow method: Soil (FF Happy Frog) - But I only have one of those 3-way meters and not sure if my soil is really beyond 7.0ph which it's showing, but then again, i may not be using it properly and seems like whatever soil i put it in (few diff kinds) it's showing between 7-8.

Feed: and supplements used: GH Flora Trio (around half suggested use for first month or so, then increased to nearly full (but only about twice per week and watering once in between with nothing but 6.5'ish PH balanced water). Started using Cal-Mag a few weeks into the grow, at about half suggested, with every feeding. BUT.... I recently learned I was using it in the wrong order, adding the cal-mag AFTER the GH trio. The GH Trio was used correctly: Micro>Gro>Bloom, but I was told to add the cal-mag after bloom and I JUST learned it should be used BEFORE (had to learn the S.N.A.P thing lol). I haven't used the cal-mag for about a week now (never used it properly yet since i learned).

water source: Tap (hard). Here's my latest local water report: https://www.irwd.com/images/pdf/services/IRWD-WQR.pdf

Strain/age: Mephisto - Chemdogging (48 days)

light used: They started out for the first few weeks under a viparspectra par600 (274 actual watt blurple) and for the past 3-4 weeks have been under an HLG 550 V2 R-spec (at 36" until flowering started, then slowly down an inch here and there currently at like 30". I never went down past 28" because I saw this happening and started to wonder if it was too much light, although they claim to put it at 24" for flower.

Climate: The tent is 4x8 (only using half of it) and stays around 67F - 80F (early in the grow i had some issues with heat which may have stressed these plants out. there was a period for about 3-5 days where my timer outlet had accidentally switched to always on, so there was a few days of 24 hour light, which caused temperatures beyond 92F those mornings and couldn't figure out why... The RH ranges from around 45-50% but they had 65%+ when they were in veg.

Additional info: I had all 4 of them on a blumat setup for the past month or so, and would put the nutes directly into the resevoir (just drips via gravity) and would keep the solution at around 33-50% of the suggested use. Since I have been trying to remedy this, I have removed those so I can gain some control here. I also just gave each of them their first dose of Recharge last night (about 10oz per plant of a 1/2 tsp per gallon solution). Oh, one other thing that may or may not be relative, a couple weeks ago these things herm'd. i saw a couple balls on one, then soon after the other 3 also showed it. i have been carefully monitoring and removing them and not seeing many show up. they have all been down below 1/3 of the plants height so far, none above that point. and currently there are none I can see (though a few rogue ones probably chillin). i just keep removing them and since they all herm'd, decided not to kill them all.

What a disaster... Thanks in advance for any suggestions/tips/advice!!!

 

[Simplicio]

I'm having similar problems with light bleaching.
I have a smaller Rspec light similar to yours in one tent, and some COBs in a different tent.
The accepted wisdom seems to be that 28 watts per sq ft is enough for the most modern LEDs like these.
If you're using half your tent, that's 16 sq ft, and the power needed would be 448 watts, so you probably have too much light.
The light intensity doesn't decrease much with increasing distance, so dimming the lights might be the only option other than not shining part of the light on the plants.

I think these powerful lights can do harm.

 

[BII]

...The light intensity doesn't decrease much with increasing distance....

Can you explain how light intensity does not decrease much with increasing distance? Unless narrowly focused and even if tent side reflectance is high, light intensity (PAR at the plant level) will be lost by raising vs. lowering lights within a tent. [How do you get around basic physics -- the inverse square law?]

 

[umop apisdn]

I'm having similar problems with light bleaching.
I have a smaller Rspec light similar to yours in one tent, and some COBs in a different tent.
The accepted wisdom seems to be that 28 watts per sq ft is enough for the most modern LEDs like these.
If you're using half your tent, that's 16 sq ft, and the power needed would be 448 watts, so you probably have too much light.
The light intensity doesn't decrease much with increasing distance, so dimming the lights might be the only option other than not shining part of the light on the plants.

I think these powerful lights can do harm.

well, considering the light is only 480w, it's not too far off. also, this light is made for a 4x4 pretty much, AND i have it higher than they even suggest. a lot of people have a lot of success with this light and i have never heard anyone having issues with it being too powerful for growing. it's what it's made for! when you raise the light, im pretty sure the intensity decreases, hence the reason they say to have more par in flower than veg right?

 

[Simplicio]

Can you explain how light intensity does not decrease much with increasing distance? Unless narrowly focused and even if tent side reflectance is high, light intensity (PAR at the plant level) will be lost by raising vs. lowering lights within a tent. [How do you get around basic physics -- the inverse square law?]

The inverse square law applies to point sources, not to grow lights.
Intensity does drop off with increasing distance, but not by a whole lot, according to my Lux meter.

Intensity is constant at any distance away from an infinite sheet of light.

A grow light is somewhere in between these two extremes.

 

[BII]

OK, so you are assuming that many, most or all grow lights focus all or most of their light down within a narrow range or footprint. But the trend to me seems to be and/or most lights now concentrate more on wider dispersion rather than narrow focussing. So many or most lights will lose significant intensity/power if raised higher.

Otherwise (back to helping with the plants), I don't see any light bleaching or light-caused issues. If anything, the leaves at different levels look rather uniformly off-color vs. the top leaves most or only affected. I suspect some issue with inadequate feeding, pH off, etc.

 

[Olderfart]

The inverse square law applies to point sources, not to grow lights.
Intensity does drop off with increasing distance, but not by a whole lot, according to my Lux meter.

Intensity is constant at any distance away from an infinite sheet of light.

A grow light is somewhere in between these two extremes.

Agreed with my experience - the response to light height adjustments was a heck of a lot more subtle than the inverse squares law would suggest. In order to get the improvement I needed, I had to dial the power down, not just move the lights. Wall reflectance may not be perfect, but it redirects a lot of light onto the plants relative to what would be the case if no walls were there, and the inverse square law assumes no walls, and as you point out, a point source, neither of which is even close to my setup.

 

[Simplicio]

OK, so you are assuming that many, most or all grow lights focus all or most of their light down within a narrow range or footprint. But the trend to me seems to be and/or most lights now concentrate more on wider dispersion rather than narrow focussing. So many or most lights will lose significant intensity/power if raised higher.

Otherwise (back to helping with the plants), I don't see any light bleaching or light-caused issues. If anything, the leaves at different levels look rather uniformly off-color vs. the top leaves most or only affected. I suspect some issue with inadequate feeding, pH off, etc.

I wasn't assuming anything, just giving extreme limiting cases.
And I said that grow lights are somewhere between these two extremes.

My guess is that grow lights can be approximated by assuming 70% infinite sheet, and 30% point source.
Only the point source part has decreasing intensity with increasing distance, and that part does obey the inverse square law.

There might exist a virtual spot that would closely approximate a section of the light's full intensity, and in that case the inverse square law would work if distances were measured from it. That virtual spot would likely be several feet above the light.

 

[ManWithWrench]

They look like they have been drinking Mountain Dew

 

[umop apisdn]

I wasn't assuming anything, just giving extreme limiting cases.
And I said that grow lights are somewhere between these two extremes.

My guess is that grow lights can be approximated by assuming 70% infinite sheet, and 30% point source.
Only the point source part has decreasing intensity with increasing distance, and that part does obey the inverse square law.

There might exist a virtual spot that would closely approximate a section of the light's full intensity, and in that case the inverse square law would work if distances were measured from it. That virtual spot would likely be several feet above the light.

So in other words, this light is too powerful for the suggested 4x4 area? And that their recommendations of 24" for flower, 36" for veg are actually not ideal for the light? It sounds like you know what you're talking about, but I find it surprising that this light has such good ratings and this is the first time i have heard anyone basically say it's too powerful for a grow tent. However, perhaps I'm not fully understanding what you're saying...