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watering frequency

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Hey Peter,

                 That question is a bit like 'How long is a piece of string?" There are so many variables. I see you are using a pump. How big is your pump, as in, how many Ltr/hr? What sort of system are you running, RTW? Flood and drain? Recirc? How big are your pots? You say 'tank water' (hmmm that can be problems.) All of these factors will contribute to the answer to your question. So to give you an exact answer is not possible, BUT...

... Here's what I do. I'm running a recirc system in a layer of clayballs(4inches) then perlite in 50ltr pots, my pump is 800ltr/hr and runs 15min/hr thru grow and flowering, using tapwater.

For a start all of my medium is washed THOROUGHLY. The dust from the clayballs and perlite goes a bit like a grinding paste, I'd reckon the dust from volcanic rock would have the same effect. Also the salts from the nutrient (nute) mix stick to the insides of pots and tubing and tubs, this can also cause the dust from the medium to stick to the nutes, so wash it well.

If you are running a RTW (Run To Waste) system your feeding should be a lot less than 15min/hr or you'll end up with a huge water bill.


Now you say tankwater, many nute manufacturers make their mixes taking into consideration mains water supplies. Mains water is treated and as such has a level of salts already present. But in using tankwater these salts will NOT be present, so although your nute manufacturer may state 1500ppm, that won't be correct as their measure is using tapwater. Now I believe there is an additive available for those using rainwater, but others who use rainwater would be able to give you a better idea on this than I. I did, once and only once, use rainwater. I saw a marked decline in the health of the plant. Admittedly my rainwater was stored in a galv tank. The galv may have caused my readings to be out, it could have altered my pH, I'm not sure. But my plant didn't like it at all. So I flushed and went back to tapwater.

Other people have also mentioned that with rainwater there may also be other 'variables'. For example bird shit on your roof and decomposing leaves and crap in your gutters. These can also alter the salt levels and pH in your water.


Hope it helps


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sorry about not giving enough details: pump is small aqua pro and 750 ltrs an hour and the system is recirc.its a 4 pot satellite system and using the smaller standard half pots that sit in a basepot where the nutrient runs through at the bottom hose. the tank is 50 litre tub. medium is volcanic rock and (well washed) beforehand. the water is tapwater but has to be dechlorinated outside for a day or two prior to using as the water here is bad for chlorine. the fact im am using tapwater is taken into consideration and the nutrient slightly reduced to accomadate for this. the solution is used for 1-2 weeks and topped up with fresh solution every 1 -2 days.(about 10 llitres) and then dumped and replaced with new solution. am using monsterbud with the nutrient.ppm is good and ph is good but was told by shop dealer to runs feeding every half hour but not sure on whether his advise is legit cos he doest grow pot?? was running red devil strain prior and was doing 15 min water cycles with blowaway results

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Yea, the powerbill is large, but so are the results lol


The wife has a big ass spa bath too which adds to the bill

I'm in 12/12 for around 13weeks, which is a bit longer than most, so the total bill is around 1500, but that's the whole property, not just the room

You pay for what you get and you get quality, that's what I need/want



Edited by merl1n
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Im running a similar system with 4 18ltr pots inside 27ltr outers, clay pebbles. My rez is also 50ltrs


I have had to dial my system in over this grow and may change a little with the next but the  biggest problem is the rez size with mine when compared to the pump.


The physical size of the pump stops you from using all the water and the amount of time it takes for water to return to the system slows as the plants roots grow. When I started flower the water took 5 to 8 mins for the return to complete but now at 7 weeks it is taking nearly 20 mins to fully return. So top feed recirc is not a continuous process as one would think.


I started with 15 min feeds cause that was the default (lowest) on the mechanical timer but as you can see by the figures in the picture below my pump ran dry nearly straight away and the amount of water drowned the plants cause it couldn't run away fast enough. So ended up getting a digital timer and now run it for 3 mins every hour of light and 2 x2min feeds during dark just to keep the pebbles wet. This means you have to have a digital timer that does 20 different times a day. to water evry half hour you would need a digital timer that does 40 times a day and I think they are rarer than chook dentists.


I think when I build the new flower system I will go for a smaller pump or a bigger rez so I can have better choice of watering time and length. IE. back to mechanical timer with smaller pump and feed every half hour.


anyway each system is different and just needs a bit of time to dial in.


here's my initial calcs for first and now in case you want the math.



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probably only need 15 mins every hour in vol. rock or clay. rock retains more water than clay balls but, if it is very hot in your room that you might need more. is your water ph adjusted? between 5.8 and 6.5 is what you looking for to keep the plants sucking up all the good stuff. any more watering can stop them growing or cause fungi probs, root rot and mould/black mildew from high humidity to name a few. it is beneficial that the root ball reoxygenate between waterings. and don't forget to flush your plants with fresh ph'd water before you finish and harvest, will just make sure all the chemicals are flushed out and make for a nicer smoke.

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