Rapidly Dropping pH -- Time for a res change?

[Dada]

Hi Folks,
I have 1 NLxBB and 2 WW in a ten-gallon DWC system with a big air pump and two 18" air wands that are bubbling like mad. Plants look perfect -- they are in day 21 of flower and they are budding all over the place. No spots, not many dying leaves except those way underneath that aren't getting much light. Temps are good and I am using a 400 w HPS supplemented by two 42 w 6500K CFLs (trying to get some light under the thick canopy). I am using the GH 3-part system and giving them the full dose for flowering plants. I have pried up the res lid -- which is no easy task because these plants have gotten BIG and heavy -- and the roots look white. Of course, I can only see the top layer and don't know if something else might be going on underneath.

Plants are drinking over a gallon a day, so I have followed advice to not change the res unless I have a problem. Now I don't know if I have a problem or not.

My pH is suddenly dropping every night. For the longest time it stayed right around 5.8. Now I am giving it 6.2 water/nutes and by the next evening at lights on, the pH is down to 5.3 or 5.4 -- in that range. I wouldn't normally fill the res with water/nutes at that high of a pH, but since it is dropping so much, I am trying to offset it a little.

PPM is also up to 2500 (starting with water that is 180). That is way high, though I don't know the reason for this jump. It happened to me one time before, though, and a res change sorted it out.

Can someone give me some hints as to what might be causing these changes? I assume a res change is in order, so I have a big tub of nuted water and a pH of 5.83 that I will add after I siphon off the existing water/nutes. Anything else I should be doing?

Thank you!

 

[Useless]

You have a build up nutes in your system.
The more nutrients that build up, the lower your PH will be.
Do a quick flush, and start with a fresh ressy. And lower the starting PPM of the solution a bit, maybe 200-300 ppm, that way your plant uses the food as fast as the water. It should help you in getting a stable solution.
A quick general rule of thumb is that if you monitor your PPM over the course of say a week, and the PPM is dropping, then your starting solution is weak and your PH will go up. If your PPM's are increasing then your starting solution strength is too strong and your PH will go down as the ferts build up. If PPM's stay steady, your mix is right on target for your plants, and your PH will stay steady too.
Hope that helps, let me know if you have any questions.
Cheers

 

[DLA]

Hi Folks,
I have 1 NLxBB and 2 WW in a ten-gallon DWC system with a big air pump and two 18" air wands that are bubbling like mad. Plants look perfect -- they are in day 21 of flower and they are budding all over the place. No spots, not many dying leaves except those way underneath that aren't getting much light. Temps are good and I am using a 400 w HPS supplemented by two 42 w 6500K CFLs (trying to get some light under the thick canopy). I am using the GH 3-part system and giving them the full dose for flowering plants. I have pried up the res lid -- which is no easy task because these plants have gotten BIG and heavy -- and the roots look white. Of course, I can only see the top layer and don't know if something else might be going on underneath.

Plants are drinking over a gallon a day, so I have followed advice to not change the res unless I have a problem. Now I don't know if I have a problem or not.

My pH is suddenly dropping every night. For the longest time it stayed right around 5.8. Now I am giving it 6.2 water/nutes and by the next evening at lights on, the pH is down to 5.3 or 5.4 -- in that range. I wouldn't normally fill the res with water/nutes at that high of a pH, but since it is dropping so much, I am trying to offset it a little.

PPM is also up to 2500 (starting with water that is 180). That is way high, though I don't know the reason for this jump. It happened to me one time before, though, and a res change sorted it out.

Can someone give me some hints as to what might be causing these changes? I assume a res change is in order, so I have a big tub of nuted water and a pH of 5.83 that I will add after I siphon off the existing water/nutes. Anything else I should be doing?

Thank you!

Yes as Useless said a little flush is needed. This is when I really like Flora Clean for those fast thorough 2 hour flushes. You could try a little Mg but only if you see any other Mg symptoms, otherwise a short flush, maybe overnight with straight water.