pH balancing new water

[lagreca]

I read in a book "It is important that any water used for refills or new batches of nutrient be pH balanced to +/- 6.0 (depending on crop) before mixing with your concentrated nutrient powders or liquids."

Is it true you should pH balance the water for the nutrient tank before adding nutrients?

Problem:
I added new RO water (pH 7.07 @ 86 ppm) to my nutrient tank last night. Then I stirred in my 3 tablespoons + 1 teaspoon nutrients (Flora Nova Grow) and the pH dropped to 5.2. I was worried this was too low for my plants, so I added 2 gallons of RO water which brought the tank to pH 5.38. 12 hours later I checked and the pH was 6.10. Why the large swing in pH overnight? How can I prevent this?

[Jonathan Dyer]

What you read was true in most cases. Hydroponic water needs to be pH buffered prior to adding nutrients or there is a possible risk that the nutrients could settle on the bottom of the tank and hence not available to the plants. When buffering try to use acids/alkaline chemicals as they don’t react with the nutrients where as natural substances such as shell grit react with the nutrient causing various chemical reactions producing other compounds that commonly precipitate out becoming non available to the plants. Additionally, this may also adjust pH levels overnight.

Generally electronic pH meters are fairly accurate if calibrated properly and left in the sample long enough to stabilise say 3+ min, however, other water based test kits can vary enough to give a false result so it may be a incorrect reading. Also make sure that the solution was fully mixed and well agitated to get a uniform pH and then take the reading.

[GaryD]

Hi,

Generally electronic pH meters are fairly accurate if calibrated properly and left in the sample long enough to stabilise say 3+ min......

And they can be hopelessly inaccurate, too. I have a Milwaukee meter and it never gives the same reading twice in row. I much prefer the freshwater test kits that use the liquid drops.

I agree with Jonathon's observations about buffering. If you don't sort the pH before you add the hydro nutrients, you run the risk of locking up some of the elements in the nutrient mix.

Gary

[gavinl]

G'day

I also run a hydro system and through trial and error and by asking many questions (about ph and cycling to both Gary, Jonathon and Lyn from Boxsell hydroponics) thought my experiences might help you a little.

I decided a while ago (due to a substantial delay in getting my sleepy cods) to go the hydro way rather than aquaponics and put the fish in my dam - although I still use aquaponic setups. In my situation, I have bore water that is plentiful, but limited rain water. The bore water is very hard and has a cf reading of 2.50 (about 1300 to 1700 ppm) - which is high (tomatoes usually need a CF level of 2 to 2.2). It takes a lot of acid to reduce the ph. I have heard that nitric acid is very good for hard water, but is extremely difficult to get a hold of. Hydrochloric acid does not work well with my water and requires a large amount to lower the ph. Lemon and Vinegar are too weak for my purposes.

I am presently using phosphoric acid with decent results. Before using the bore water with my system, I control the ph first. I have a 900L tank that I fill up with bore water. I add acid every 2nd or 3rd day and test with normal ph drops - I haven't found ph metres that great...although EC metres are very handy. It takes about 10 to 14 days for the ph to stabilise, but once it does it is fine for about 3 weeks...which is about the amount of time that I need before swapping the water and putting in new nutrients. When initially putting in the acid, the water will go a little milky, which seems to be an indication that it is reacting with the nutrients and minerals already present in the bore water - this doesn't last more than about 3 days.

The good news is that I only use about 300 litres of PH stabilised water for my flood and drain hydro system and about 50 litres for the NFT system. I might need to use another 50L on the NFT during a two week period - I swap the NFT water every two weeks. I sometimes add another 50L also to the Flood and Drain system, which I change every 3 weeks. I use the 'old' water to fertilise my citrus trees and garden.

I've attached a few pictures, which might help as my explanation isn't that concise. The first picture is of the flood and drain tank. The second photo is the PH stabilising storage tank. I would also suggest that you get a nutrient mix that doesn't lower or raise the ph too much - many are designed for this. Ask at a hydro store and they should be able to help. Additionally, don't be afraid to experiment a little. I was advised by a hydro store that my bore water would probably not be suitable due to the high CF reading. My NFT has a CF of approx 4 (2.5 from bore water + 1.5 from nutrients) and my flood and drain of about 4.5 (2.5 from bore water+ 2 from nutrients). I had the water tested and have been told that it is fine for drinking...it just has a lot of minerals. So far my vegies have tasted great.

Hope this helps

gav

[Hamish]

Hi Gav - in your second photo - what are your plants sitting in - are they suspended in the tubes with mesh baskets - or are they just sitting in the tube - any chance of a close up shot of how the plants are held in the tube? What are you growing?

[gavinl]

Hi Hamish

No worries mate, I'll get you a close-up photo tomorrow. The plants are placed straight on to the tube. I have the angle of the NFT on a fall of about 2cm per metre. This allows for the water to gently trickle past the plants' roots system and into the water tank at the bottom. If I have a really small or spindly seedling, I will put masking tape over the hole and poke a whole into it. This gives some support for the first week or so, then it can be removed. It also helps to reduce any algae build-up by keeping the light out.

The mint on the left side of the photo is planted in a pot plant with clay balls. It is suspended over one hole by the 'pot system' that boxsell sell. Basically, a separate spag line is used to drip water into the pot plant and the run-off is collected in the whole and continues down the tube. The mint loves it and it prevents its roots from taking over everything and blocking the tube.

I'm growing heaps of lettuce varieties - nearly everything but iceberg. Soft herbs such as parsley, oregano, rosemary, basil, coriander and thyme all grow well. I use the same nutrient for lettuces and herbs at about 1.5 cf and about 6 - 6.5 ph. I am constructing a new NFT system at the moment and will try to grow toms and cucs at 2.2 cf - it will be interesting to see how it goes.

gav

[lagreca]

Thanks for the comments. My reservoir is 12 gallons of liquid, and big enough to hold about 20-30 gallons total.

It seems as though the water likes to return to its original pH before nutrients were added. If I put Mad Farmer Get Down in, the pH will lower, but eventually creep back up, and I have to continually add the Get Down.

6/29 @ 10pm = pH 5.38
6/30 @ 2:15pm = pH 6.10
6/30 @ 8:15pm = pH 6.09
7/1 @ 9:50am = pH 6.29

Also...

I'm wondering if this is the reason to pH balance the water to 6.5 before adding the nutrients?

Lets say your target nutrient level for tomato's is 2200 PPM. If you use hard water that originally had 800 PPM, would you add the two together for a goal of 3000 PPM, or just bring the 800 PPM up to the target of 2200 PPM?

Right now it's not that critical, because I'm using RO water that starts off with very low PPM, but I'm just curious about using tap water.

[Jonathan Dyer]

Guys I frequently use my electronic pH meter (testing general water, hydroponic & aquaponic water, winemaking/beer making) and I find them to be accurate within 0.2, I am frequently recalibrating and cleaning the electrode so I think that helps, if you are spending less than $100 I wouldn’t recommend it. I am also doing the same with my 2 different types of EC meters (one only displayed in ppm) and find them to be very accurate. I had to recently replace the electrode on one of the EC meters (the one in ppm, the better one too) as I knew it was giving me a false reading and I could taste much more acutely and that alone cost me $80 to replace (just the electrode) so same story applies electronics need good maintenance and need to be reasonably pricy to be any good for long periods of time.

What really matters most in water is the concentration of Sodium Chloride (NaCl) in g/L (of pure NaCl). EC meters test the hardness of water by measuring the amounts of total salts as TDS (Total Dissolved Solids) and can be expressed in ppm, ppt, millisemens and a few others. NaCl is what will have a adverse affect of many plants well before calcium carbonate, magnesium sulphate, magnesium carbonate, iron sulphate just to name a few will cause harm to plants as plants require these compounds to grow in much higher concentrations than that of common salt. An expression of total NaCl g/l is the most accurate way to differentiate between the two. All of these compounds dissolved in water add to the overall concentration (ppm) the more of the compounds desolved in the water the higher the reading. So just remember if you have a high ppm reading it may well not always be a ‘bad’ thing providing it is low in NaCl concentrations, it may be very beneficial in some cases (providing it is not excessively high as this can cause toxicity and stain marks on buildings) for your plants as the plant requires the elements to grow and fruit meaning less fertiliser to apply if at all. Although I will say it is very common to find a high EC reading caused almost solely by NaCl, but you can taste easily the difference between what is what.

On my property I am happy with bore water very high in Epsom Salts (magnesium sulphate) as our soils are relatively deficient in both Mg & Su by which the plants use all I can put on and I still have to apply more of this stuff.

For some reason hydroponics act differently to soil bound plants in general if you were growing soil plants especially beans (and I mean especially beans) readings of 1300 to 1700 ppm would not be very suitable if no technology like magnets were employed (where beans would be almost dead) and others would struggle bar a small few; soils play an important part where sand is most suitable for these getting much worse as the soil moves towards clay. I would say these readings would be well within reason of growing plants hydroponically but, anything over 2000ppm would be pushing it. I have had EC readings of 1500ppm and there has been zero visible setbacks as I’m taking you have also found Gavin. Depending on the NaCl concentrations Gavin I think your tomatoes should be ok go with what looks and tastes right.

Lagreca sorry to be stupid what is RO water?

[GaryD]

RO water is water that has been through a reverse osmosis system.

[lagreca]

I'm sorry for not clarifying. RO is my shorthand for Reverse Osmosis. I have a system at my house to create drinking water, and since my hydroponics system is so small, I can generate enough water for it too.

Here is a link to: 2007 San Diego water quality report

There is also this: Additional Physical, Mineral, and Metal Characteristics report

I am in the Alvarado district. Do those reports show enough to tell if my water is good enough for my hydroponics system?