Backyard Aquaponics
A place to discuss aquaponics

I was talking to some people that think that lime-stone can be used as a meidum and it will not buffer the ph too high, in fact they say it my be some benifit. That it would keep the ph stable no mater what and some micro-orga-thingys will use the calcium as food. I do belive that when the bio film coats the rocks that they will become pretty stable.

I remember someone on this fourm saying it would cause more harm than good to use limestione, However, it is the most pratical by far of any meidum for me to use and i was wondering if this type of thinking is still the stance of the fourm or if it actually can work.

I am curently useing floating raft, not getting the results i would like, fighting root rot. Plus, it limits the types of plants i can grow and i want to plant many different types.

What do you guys think of useing a limestone bed. I would love to do a small run but i only got a big system now. so i would like to be sure before i take the next step and get a truck load off gravel to wash and then it doesent work.

We have very hard water and 20% of my gravel is small limestone chips. The pH never goes below 8, even with the addition of vinegar. Algae still manages to swing the ph about .4, but I understand that is a different mechanism than the traditional acid-base-buffer reaction.

It can be done (anything can be done if you really want to and have the resources) but here are some of the drawbacks.
Certain nutrients will likely be locked out and you will therefore probably need to foliar feed (spray the plants) with those nutrients on a regular, perhaps weekly basis. Iron is the main one but I'm sure there are some others that might be needed too at that high a pH.

Some fish and bacteria are not as happy at that high a pH either.

And big drawback is that ammonia is way more toxic at a higher pH than a lower one.

My pH experience is mainly with the use of shells that buffer to a pH of 7.6 and so I am living with it. I have not been successful with certain types of plants in the system though as the pH seems to be too high for them and nutrient deficiencies have stunted or killed the cucumbers, slowed down the strawberries, made the nasturtiums look strange, wiped out the gourds, done in the melons and probably stunted some others that never came up. Tomatoes, onions, lettuce and herbs all seem to love it. Hot peppers surviving but not thriving.

As far as the biofilm stabilizing it, I wouldn't count on that helping you have a pH anything different than what the limestone naturally pulls the water to. Does anyone have an exact number for what limestone buffers to? The point about bio-film coating and stabilizing stuff is probably more an issue to people who are battling the low pH with a small amount of shells or limestone. If you were to put a small amount somewhere in the system where the water is not being forced through it, then the buffering effect could be nulled out by it being coated with bio-film and not being effective enough.

Well, most of my research shows that the pH would be too high for Aquaponics. i Just manage to source coco coir in a large quanty so i will use that for now.

CG... a combination of coco-coir and limestone growbeds might balance the pH to an aceeptable level....

i.e .. the limestone will probably buffer toward pH 7.5-8.0.... on the other hand the coir will tend toward pH 6.0-6.5......

Put them together... and theoretically you should get the "normal" carbonate buffering effect that many strive to acheive with the addition of shell grit etc...

i.e a pH of around 7.0-7.5....... depending on relative volumes etc....

It might be worth a try

FYI, I added a layer of limestone to the top of each of my GBs as the gravel (blue steel which is dark colour) absorbed too much heat which was effecting all seedlings.

I didn't wash the limestone before I put it on and the limestone dust raised the PH to a stage that it killed my fish.

I still have it there and my pH is constant around 7.0

Simon

Are you saying Simon that if you had washed the limestone gravel - so no dust - that the fish would have lived? Did I understand correctly that you are still using limestone with new fish?