PPM and pH decreasing?

Regarding changing nutrients; I have read that if PPM increase and pH decrease - add ph'd water, if PPM decrease and pH increase - add nutrients (increase PPM), and if PPM and pH remain stable - don't change anything. Problem is that my system is a combination of both recently. PPM decrease every day and pH also decreases every day. For example; two days ago my PPM were 390 and ph was 5.9, the next day PPM: 365 and pH: 5.7, today, PPM: 340 and pH: 5.5.


This pattern has been going on for a couple of weeks. The plants are now drinking lots of water so I am adding 5 gallons every 4 days or so. Each time I add 5 gallons, I also increase the nutrients up to about 400 PPM. I don’t go over this because last grow every time I increased the PPM over 400, the plants would show signs of burn. Even during flower I could not get over 400 PPM without signs of nute burn.


This is my second grow, Granddaddy Purple (4 plants), DWC (5 gal per tote and another 10-15 gallons in a control res so 30-35 gals total), about week 4. They have been topped a couple of times so growth has been slowed a little but they look very healthy (see pic).


Some of the top growth has 11 leaf fans so I think they like the nute schedule so far but what do you folks think about the PPM and pH both decreasing every day? What does this mean?

That's usually a sign of too much Nitrogen, try cutting back a tad on the nutes instead. PPMs dropping means your plants are taking in more nutes than water. You want them to take the same amount of water/nutes.

n0thing said:

That's usually a sign of too much Nitrogen, try cutting back a tad on the nutes instead. PPMs dropping means your plants are taking in more nutes than water. You want them to take the same amount of water/nutes.

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I have been getting a little bit of leaf curl so I have been cutting back on the nitrogen - I'll cut back even more and see if that helps. Thanks for the info.

Critrgitr said:

I have been getting a little bit of leaf curl so I have been cutting back on the nitrogen - I'll cut back even more and see if that helps. Thanks for the info.

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This may help you

*The ideal scenario you are looking to achieve is where the EC is either dropping slightly or remaining static, with a static or slightly rising ph and a dropping water level. If you get this situation, keep doing exactly what you are doing because your plant is feeding and drinking.


Note 1.
When pumping air into a nutrient solution in order to add Dissolved Oxygen, not only oxygen is present, CO2 is also pumped in. If you live near a busy road, this may be higher than normal, so you may get a dropping ph quite often. I have noticed most of the growers who suffer from a falling ph in DWC tend to live in large cities. This may not be a link but it could be.
When CO2 is added to water, it makes it more acidic. This is the precise process which causes acid rain, pollution from power stations etc pouring CO2 into the air, this mixes with the water vapour in clouds causing acid rain.

Note 2.
Most people assume that with a rising EC, it is the plants way of saying, I dont want more food, here, have some back.
What is actually happening is this.
Plants roots take in water/nutrients through a process called Osmosis. Effectively, if you think in terms of the roots having their own internal EC.
The osmosis process will always try to balance out the EC's, taking from the higher side of the barrier and giving to the lower part.
So if the EC of the nutrient solution is higher than the "internal EC", then food & water will flow from the solution to the roots, this is the normal process.
If however, the EC of the solution is higher than the "internal EC", then the balancing will work the other way and nutrition will be leeched from the roots to the solution.
A res change or increase in EC should resolve depending on the other factors such as ph and water levels.

Note 3.
Nutrients flow around a well hydrated plant much more effectively and faster than one which isnt as well hydrated.
How can growers use this?
By feeding at lower levels, the plant needs to take on more water in order to get the nutrition it requires.
So by feeding at moderate levels, this forces the plant to drink more.
By drinking more, it is better hydrated, because it is better hydrated, it needs more food, making it eat more.
So feed at moderate levels rather than overly aggressive levels.
The method of pushing the EC until you see signs of nute burn is damaging to the plants and although many growers use this method, I am not a fan though your plants are not mine!

Wow, that is great info!

I was experiencing the last line on the chart and ironically, I did what it said - I changed the water out with increased EC water. Now I have basically stable pH, decreasing water and EC daily so it looks like I am in good shape.

Thanks for taking the time to post this.