Backyard Aquaponics
A place to discuss aquaponics

Hey guys,
Quick insight on my situation, I am battling 6.0 or less pH so I went out and purchased a 50lb bag of garden lime (see link below). Anyway, I was reading a thread somewhere and one of the posters said to not use Dolomite lime. Is this true? I am going to add seashells to the system tonight when I do a water change, but I was hoping for a quicker pH change. The fish are going into a separate holding tank while the system is buffered. The pH of the tap water I am using is 7.8-8.0 depending on time of day. I treated 50 gallons of tap water yesterday afternoon with Vitamin C to de-chlorinate the water.


Garden Lime purchased : http://www.homedepot.com/p/Sunniland-50 ... /100199340

No you need slacked lime the white stuff they use in concrete
But use it sparingley till you get the hang of it in 5000 liters i used one cup full every 6 weeks

No harm in using garden lime, it will have the same buffering effect as using sea shells as they are both basically calcium carbonate but because garden lime is (usually) just ground up limestone rock it will dissolve into solution quicker and therefore correct your pH quicker, the dissolve ions will also add hardness to your water which can aid fish health if your water is too soft (i.e. rain water).

If you want instand results use the slacked lime like F&F suggests but the garden lime will give better long term buffer capabilities.

Simo - thanks for the response. I have been having a lot of troubles lately with my system all around. Are you aware if this garden lime inhibits bacterial growth by any chance? Just out my newly added water change of Vitamin C treated water is...

As Simo says garden lime is just crushed limestone, and may contain a few other minerals such as magnesium, and is a good buffer.

Slaked lime is completely different- it is Calcium Hydroxide, a very caustic substance, or alkali, and wont really provide any buffering action, as it will neutalise any acid present straight away. Be careul about getting it on your skin or in your lungs and eyes too, as it will cause chemical burns.

All carbonates will buffer PH and add carbinate hardness..(calcium carbonate, potassium carbonate). Hydroxides will also buffer PH.. (calcium hydroxide, potassium hydroxide) although hydroxides are a much stronger PH buffer. Brickies lime (slacked lime) is a calcium hydroxide and can only be used sparingly.

In my system the pH is constantly dropping despite a heap of small shells and crushed limestone that I have included in the water flow. I have now resorted to a tablespoon of hydrated lime every day or 2 (depending on how much I'm feeding) to maintain the pH at about 6.5.
This disturbed me a fair bit and I wondered what was going on. Then a few weeks ago I read Dr Wilson Lennard's Aquaponic fact sheet on system water chemistry http://www.aquaponic.com.au/Water%20Chemistry.pdf and while you are there check out the rest http://www.aquaponic.com.au/fact%20sheets.htm

Quotes from Aquaponic fact sheet on system water chemistry

and

And


Now it make a whole lot more sense to me.

While this has been said one way or another on the forum the fact sheets puts it all together in one place.
If you get a chance, read the other fact sheets.

Fish Tank Size & Shape --- Dr Wilson Lennard - Background --- Media Beds & Sizing (Ver2.0)

Fish to Plant Ratios --- Solids Filtration --- Basic Water Chemistry

Thanks again for the advice. Glad to see I can use Calcium Carbonate, as I have a 50 lb bag of it. I will have to read those pdf's tonight, they seem very interesting and filled with info.

As for potassium, do I need to be adding this to my system as well? How would I test for this in my system to know how much to buffer?

I only add potassium bicarb every now and then to cover possible deficiencies. For my system that is a desert spoon per bed per month. I have not noticed any potassium deficiencies so far.

Calcium carbonate may not give immediate increase in pH and so some hydrated lime may also be useful to keep the pH where you want it. I have had significant quantities (3-4kg) of Calcium carbonate (ground limestone and small shells) in my system for well over 18 months and that did not stop my pH from dropping to below 6. IMO I would use both, the Calcium carbonate for long term buffering and hydrated lime to keep the pH were you want it when the pH drops.

You should alternate between a Calcium and Potassium buffer...

How much to add depends on the strength of the buffer, and size of your tank...

You shouldn't move pH by more than 0.4 points in any one application...

A general rule of comparative strengths of buffers... Hydroxide>BiCarbonate>Carbonate...

Marc thanks for the advice. I will have to order some online as my local hardware stores don't carry this hydrated lime, only the crushed limestone. Could I possibly build up a layer of shell rock on the bottom of my sump tank, which my pump would rest on and be pulling water off of? I am hoping to build some type of physical buffer system, so I do not need to be adding lime to the system all the time.

You'd be better off getting some "Shell grit"... and suspending it under a water return....

Shell grit will act as a slow release buffer... so if you pH is low 6ish... you may need to buffer it back a bit.... garden lime will do if you can't get anything else... (not Dolomite)

i know the suspension of shell grit under the water return is suggested by many people, however i have 4 stockings full in the water return and they did not raise the pH for me. it may work for some people but not all. My suggestion is to work out what works for your system and use it.

FWIW It is possible that the shells in a stocking does not work for me because i use rainwater and my feed loads can be high - over a kilogram per week. It is the nitrification process that is driving the pH down and that is linked to the wastes produced and the food fed. the disolving of the shells is not happening quick enough to maintain or raise the pH.

my 2c worth.

Yep... you're right...

I had similar circumstances: 1kg of shell grits placed in the flow of water wasn't dissolving fast enough to stop the pH from dropping into 5.x, so I added a pure limestone block (free from my friendly local limestone block supply) 30 x 10 x 5cm (you can compute the surface area yourself if you like) and now the pH stays consistently at 6.8 and the plants haven't been happier!

BTW I left the shell grits in the system too, so there are two buffering materials.