Hi Guys, I hope someone can help, I have built a trough type system that holds 25 gallons or 110 ltrs + on top of the trough sits 3 seats these hold the pots, there are 3 water pumps sitting in the 25 gallons, attached to a timer and switches on every hour for 5 mins, this feeds the spray bars on top of the pots, I have an air pump with 2 x 3 “ / 75mm air stones, as well as a spare water pump pushing the water round in the trough.

The feed is General Hydroponics, Total Gro & Total Bloom, EC 0.7 (T/Gro) I add Bio Bloom, PH to aim for 5.8 but not yet reached.
18 hrs cycle, Just Introduced them to HPS
Water from Tap PH 7.4
Closet Grower

Age of Plants 3 weeks from seed after hatched (Feminised PPP)
Size around 4 inch or 100mm

I use Hydroton Clay Pebbles (Substrate) PH neutral, through inexperience used Rockwood 6” / 150mm blocks, and this is what the plants rooted into, but because of the volume of rock wool I used it raised the PH, so I had to remove 90% of the rock wool, and it did knock the young ladies a little,
Initially when I made up the feed the PH naturally went to 6.8, however after it went through the rock wool found it going to 7.2 over night, so a recap the 6” blocks of rock wool sat in the bucket full of Hydroton Clay Pebbles, (I aint good at this) this is there final resting place.
I removed 90% of the Rock Wool, I replaced 80% of the feed, but I am still struggling to get the PH down, I added 25 drops of Phosphoric Acid and left it over night on checking the PH found it to be 7.0, I do-not want to add more Phos Acid just to find it isn’t doing anything, have been told that if I don’t get the PH right this will effect the development of the rooting system, there is nothing else either in the water that is Alkaline nor in the Pots.
I did test the Clay Pebbles but found them Neutral PH, I did test the Rock Wool and it raised the PH.
I am lost; do I do another water change? In my mind that is all that is left, can some of the r/wool fibres be still in the water or perhaps in the pots or am I way of base.
There it is guys
Help me 420 you’re my only hope …………
G

Do you stand your water for 24hrs before adding anything as ph straight from the tap aint a true reading

If you dont there could be your problem

My ph straight from the tap is 6.6 but when stood it reads 7.6-7.8

Owd

Hi Gazz,
no worries mate.Just knock your nutrient solution to your desired ph level.You've only used 25 drops of ph down in 110ltrs,which isn't much at all. Incidentally,it's better to use nitric acid rather than phosphoric when adjusting ph in the veg stage.

I use rockwool & pebbles.
I have never had a problem with the inert rockwool.
BUT the pebbles are a different matter.

Did you wash them really, really well when you brought them. (pebbles are filthy) ?
Did you let them settle a day in PHed water?
They then take on that PH setting.

If you do these two things it will help.

That's interesting Owderb,my local water ph is @7.2 straight from the tap and go's up to 7.6 overnight.

Owderb thanx for this I don’t stand my water, but I will from now on,

Dr rockster was a little worried about adding more acid, but will add a little more, any Idea how many drops is good, I have already added 25, how much more before it is bad for the plants?
Thanx for the tip regarding Nitric Acid, I didn’t know this.

Dyls I did wash them very well, in fact it took about 24 hrs, red dust from them, but even after a continues rinse for 24hrs there is still some red dust in the bottom of the trough.

I cant understand what is holding or buffering the PH level, but will fill a bucket of water for 24 hours and see if the PH goes up, I hope it does as my troubles then will be over, I can at least say I know the cause, will order Nitric Acid ASAP.

Again Thank You all..........

hi matey, dont know if anyone said this yet but in rockwool you need a ph of 5.8 and only rockwool needs this low ph.

Try using a pipette to put in your up and down. It means you know exactly how much you're giving them. In my setup I dose the res with between 0.25 and 0.5 ml the stir my 60 litre res and leave to stand for half an hr, then re-test and repeat if needed.

Nice one on the Nitric acid, makes sense.

Hi gazz.n

I use an nft system with the plants in troughs and in rockwool there is a 70ltr tank and the pump is on 24 hrs a day. I change the nute solution in the tank every week. I set the ph at 5.6.

Within a few hours the ph goes up to over 6 so I bring it back down. this goes on at ever lengthening intervals until about the 3rd day when the ph is fairly stable and I keep it at about 5.8 to 6. At the end of the week I repeat.

My own theory (and it may be complete bollocks) is that at each point that the ph is at the plant takes up different nutrients so going from about 5.6 to 6.2 gives the plant every opportuity to take up everything you give it.

So far I've done 6 grows and I've had many problems but none of them to do with nutrients

hope this helps

Thanx for that turnip, and when you think about it, you do make a good point in lowering and rising the PH, it makes sense to me,
Regards
G

Turnip, you say your pump is on 24hrs , does this mean your feeding your plants continuously ? I ask becuase I thought about doing that, but ended up with a minute timer, every hour there fed for 5 mins

If it aint broke dont mend it mate

Owd

gazz.n

Yep, pumps on 24 hrs. I have troughs, about 4ft long, 6ins high and 6ins wide, into each trough I put a spreader mat (probably not needed but it starts them off) and 3 plants, each in 3in rockwell cubes, then pump the nute solution in one end and drain off back to the tank at the other.

It might not be the same system that you are using but it is simple and works for me