Murray

EC = Electrical Conductivity

49 posts in this topic

my system ph sits between 6.5 and 6.8, the system is nitrfying enough to consume the carbonate hardness in the source water and reduce its ph to this level (and beyond),  so should not be causing lockout.  However in doing so most of the buffering is in Ca form with limited opportunity to use K based buffers and so get K in the system.

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Quite possibly Ravnis, though then I'll be back on the supplementation tail chasing merry-go-round :)

 

I have been supplementing K with a combination of MKP (due to zero phosphate readings), potassium bicarb (when my ph drops to 6.5) and potassium sulphate (when I appear to have K deficiency though have a phosphate reading of >2ppm and ph is > 6.8)

 

You do get a lot of K with KNO3, though it would marginally compound the already excessive nitrate issue.  

 

There appears to be enough advice (John, Paul) suggesting there should be enough nutrients in the fish food, though what appears to be my issue is that the high calcium bicarbonate content of the source water coupled with high evap rates means I cannot buffer with potassium based buffers enough to get the required K into the system AND I will accumulate excess Ca in the system which may further lockout what K is there etc.

 

So supplementing K may be a bit of a band aid, and dealing with source water the cure.  Hence why I asked John whether he meant using RO filter or finding a softer water source as the way of 'addressing hardness/ph of top up water' 

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you could use Potassium Chloride... doesn't have the negative additions of nitrates, phosphates, sulphates etc...

 

The small amount of chloride ions are actually beneficial to fish osmotic blood balances and slime coat production.. while not being high enough to impact on plant processes...

 

And wont alter your pH... would reflect to a small degree in your EC though.. ;)

Edited by RupertofOZ (see edit history)

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I'm struggling to find any Kcl, other than in 25 kg bags which might be a bit much! Not sure if the stupid wa fertiliser rules mean it can't be sold unless via Ag supplies. Certainly can't get it at nurseries or bummings. Would hydro shops sell it? Would probably cost the same from them for 1 kg as 25kg from Ag supplies though ;-)

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Just for you Matty...

 

Pretty expensive..

 

http://www.melbournefooddepot.com/buy/potassium-chloride-powder-1.5kg-bag/F00538

 

Much cheaper (so not completely sure about it)... 52.45% potassium and 47.56% chloride

 

http://www.vetnpetdirect.com.au/VPPOTCL

 

Or these guys... also contains 0.5%  Magnesium Carbonate... ;)

 

http://au.evitamins.com/potassium-chloride-powder-now-34075

Edited by RupertofOZ (see edit history)

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Thanks John, I might as well get a 25kg bag for $26, anyone else in WA want some KCl :)

 

http://www.mircobros.com.au/shop/product/muriate_of_potash_25kg/664

 

Though this seems to be going back down the supplementing path you cautioned against? rather than addressing the source water problem.  Did you mean RO treatment to address the water or just ph correction with something like HCl to use up some of the carbonate buffering?  I tried that last summer with limited success and came to the realization I may as well just add KCl in that case! (rather than add HCl to lower ph then potassium bicarb to raise it!)

 

My calcs show 1ppt of salt (what I run my barra system at) gives 394ppm of Na and 606ppm of Cl, so I would prefer not to go much above this level of Cl in the system to avoid its toxicity effect on plants (could probably go double without too much problems though as no strawberries/beans).  

 

By my calcs (using hydro buddy) this means I could add up to 1.91kg of KCl to a 1500L system to get the same Cl concentration of 606ppm and also get 668ppm of K to boot - see why you suggest it now, thats a truck load of K!  This is way more than I'd need!!! so if I was shooting for say 20ppm of K addition per time (per fortnight for instance), this would give 18ppm of Cl addition (by adding 57g of KCl).... which would take 33 additions to get to 1.9 kg (67 weeks) and that level of Cl (assuming none of it was consumed) 

 

How much Cl would plants use , if this was used continuously over time, would Cl accumulate to toxic levels eventually - it would seem to take several years if no water exchange happened, so probably not an issue?

 

What ppm level of K would you suggest I supplement to ?

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If your nitrification is consuming your carbonate hardness...as your pH indicates.. then top ups with your source water shouldn't be presenting a problem.. ;)

 

Your concern seems to be more Potassium related.... and yep, potassium chloride provides a lot of potassium without any great detrimental effects from the chloride... ;)

Edited by RupertofOZ (see edit history)

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I think the issue is that I then end up with high Ca levels (200ppm) which then upset the nutrient balance.

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Why are your Calcium values too high?... is it perhaps also related to your elevated nitrate levels...

 

Perhaps you need more plants... ;)

Edited by RupertofOZ (see edit history)

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its possible, though if that was the case wouldn't that issue arise in all BYAP off the shelf systems?  Mine are densely planted and not that heavily stocked, eg 3 off 2x1m beds (1200L filtration) being driven by 25 fish at about 40-80g / day.

 

however, what if adding more plants proportionally increases the evapotranspriration rate more than they increase Ca consumption?  In this case the Ca level would further increase due to the problem being high Ca in the source water.  

 

Instead of more plants I should be able to feed less and see if the nutrient deficiencies go away... sounds counter intuitive though be be right.  What feed rate would you typically use in a fully planted 2 bed BYAP system?

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Hi Matt,

I had a quick look at your hardness calculations on backyard aq. you have not got it quite right yet.

 

GH 430 ppm CaCO3

Ca+ 220 ppm CaCO3

this means by simple subtraction your Mg+ hardness will be 210 ppm CaCO3

to calculate the actual amounts of product or element is the tricky bit

 

You need to have a number for the molecular mass (g/mol)

CaCO3 is used as a benchmark  because it is a nice round number (100)

 

Calcium Carbonate = CaCO3 = 100.0869 g/mol
Magnesium Sulphate Heptahydrate = MgSO4.7H2O = 246.47456 g/mol (epsom salt)

magnesium sulphate = MgSO4 = 120.366 g/mol
Calcium Chloride = CaCl2 = 110.984 g/mol
Chlorine = Cl = 35.453 g/mol
Magnesium = Mg = 24.305 g/mol
Calcium = Ca = 40.078 g/mol
Carbonate = CO3^2- = 60.0089 g/mol

Magnesium chloride = MgCl2 = 95.211 g/mol

Magnesium chloride hexahydrate = MgCl2 · 6H2O = 203.30 g/mol

 

so the 210ppm Mg hardness reading will be the equivalent of 252 MgSO4 in solution (120/100*210)

 

50 ppm elemental Magnesium (24/100*210)

 

you can see from the salt crystals in the list that they have water bonded into the crystal structure that adds to the mass,(the epsom salt for example) this needs to be taken into account when you weigh them.

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Or simply 210/4.12= 50.97mg magnesium ;)

This is only right if you are sure that your calcium hardness is s 220mg.

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Haven't we had this discussion before?

The Calcium as Ca2+ can't be 220mg/L based on your General Hardness of 430mg/L.

one of the two measurements is incorrect. 220 as Ca2+ would yield 220*2.5= 550mg/L as CaCO3 hardness.

The most it could be is 430mg/L / 2.5 =172mg/L as Ca2+

 

Right  or wrong?

Edited by SwedeAquaponics (see edit history)

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that's right, if the test chart is showing calcium ions, which it is.

 

the only thing I can think of is to test the test kits. it can be very frustrating when this sort of thing happens.

 

use some distilled water and make a known concentration of calcium and one of magnesium.

 

it could be the solution concentrations are not correct for the reagent or the titrate or they forgot to put the metal inhibitor in the reagent so it is still measuring GH and not just calcium

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I was just thinking this morning, while on my second coffee there may be a way to make use of that 25 Kg bag of potassium chloride if you do buy it.

 

it would be technically possible to use cation resin beads (used in a salt recharge water softener) to exchange some of  the calcium and magnesium ions for potassium ions.

 

the beads would have to be in a fine mesh bag, perhaps in a bucket with holes in the bottom so water can flow through.

 

the way it works is kind of weird, in hard water, Ca,Mg and to a slightly lesser extent Fe and Mn will exchange places with a potassium ion for a spot on the surface of the bead. When the bag is flushed in a bucket of brine the opposite will happen and the beads shed most of the calcium and magnesium and recharge with potassium ions, give it a quick rinse in fresh water and throw it back in the recirculating tank.

 

the majority of water softeners recharge the bead with sodium chloride (the sodium sticks to the bead and the chloride stays in solution with the removed calcium) but the same bead will work with potassium chloride. the efficiency will be slightly less. I am a bit hazy on the exact ratios but I think that the bead will have to release 2 potassium ions to pick up one calcium ion (single vs di-valent bond and all that)

 

the ideal solution would be to steal/borrow/sponge your source water from someone with a KCL water softener installed at their home, unfortunately they are few and far between, I have only seen two, both owned by people who were on a severe sodium restricted diet.

Ravnis and RupertofOZ like this

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I am a bit hazy on the exact ratios but I think that the bead will have to release 2 potassium ions to pick up one calcium ion

 

The suggested, preferred ratio for plant uptake balance is 2:4:1.... Calcium:Potassium:Magnesium... or 1:2:0.5 .... ;)

Edited by RupertofOZ (see edit history)
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The suggested, preferred ratio for plant uptake balance is 2:4:1.... Calcium:Potassium:Magnesium... or 1:2:0.5 .... ;)

What's the source for this ratio?

Thanks

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looks like it'd make a good tomato source ;-)

 

Like your lateral thinking Yahoo - I'll do some more looking up on it, not quite sure in my mind how you initially charge the bead with the KCl -

 

All my systems are topped up from top up tanks so I can control the amount of 'softened water' going in and maybe alternate fills of the top up tank to get more in line with the 1:2:05 ratio John's posted.  I'm guessing my ratio at present is more along the lines of 4:1:0.5 - will be getting test kits of K and Mg soon so will hopefully get a better handle on it...  My source water Ca:Mg ratio is around 4:1 so I'm not sure if that would leave me low on Mg or whether fish food will provide some Mg.

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I just checked with Mr Google and I was right, if all of the calcium ions are removed by the resin beads there will be twice as many sodium or potassium ions taking their place.

 

I pinched this example from somewhere?

Typically, a 15 litre unit regenerating with 160 g/l  of salt will produce 4500 liters of treated water with a feed of 200 mg/l  hardness. I'm not sure I totally trust those numbers but it is a start.

 

 

 

Like your lateral thinking Yahoo - I'll do some more looking up on it, not quite sure in my mind how you initially charge the bead with the KCl -

 

new beads are precharged with sodium so I guess we would need to run some hard water through them and then brine them with the KCL solution.

 

Looking on the interweb I see there is a commercial product for freshwater aquariums called soften water poly resin. Looks like they put the bag in the filter somehow.

 

its a 350 gram bag and they are saying to recharge mix 5 tablespoons of salt in 2 litres of water and soak  the bag for 5 minutes (treats up to 150 litres).

 

A water softener will cycle the brine through the resin canister for 1-2 hours to recharge, I would be leaning more towards that timeframe rather than soaking for 5 minutes. I guess more resin means a huge increase in surface area to recharge and things like iron take quite a bit of persuading to remove from the resin. I am almost certain that the bag would stop working in just a few dozen cycles in aquarium or AP water from organic contamination but it should last for 1000-2000 cycles treating the source water.

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Murray, 0.2 - 2.0 ....... of what units (ppm or uS/cm or something else)?

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Hi Ainesh

Welcome to APN/HQ

12 hours ago, Ainesh said:

Murray, 0.2 - 2.0 ....... of what units (ppm or uS/cm or something else)?

Murrays original post is 9 years old, and he very rearly visit the forum these days, so I wouldn't expect a fast response to your Q above.

 

cheers

 

 

Edited by ande (see edit history)

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