Backyard Aquaponics
A place to discuss aquaponics

I have x2 large blocks measuring about that but bigger - approx 40x20x15
They have heaps of moss on them - would they be fine with a pressure wash ?

I have been adding over 2 tablespoons of calcium hydroxide - builders lime to my system every week, and the ph barely moves !
I also add a dessert spoon of potassium carbonate - eco rose every few weeks, that stuff is expensive...

Dunno why I can't get the ph above 6... system is going great guns though...

Pressure clean off the crap, then do a vinegar test; pour 25mL of vinegar in a single pool on the pool and notice if the vinegar bubbles and fizzes (CO2 being given off). If the reaction is (relatively) "violent" then you've probably got pure limestone, but if the reaction is subdued, you've likely got a reconstituted block which could contain contaminants from the manufacture process and I wouldn't be using them in my system. You can compare the differences in reactions by doing a tests on known substances.

Personally I wouldn't be using such large blocks, but if you've no safe method of cutting them, then you'll have to use what you have. Position one block somewhere in the FT/ST where it wont disturb the natural flow too much and where no solids or gunk can get trapped underneath/behind. If one block doesn't perform well enough, consider adding the second, but I am going to guess the surface area of the first block should suffice to buffer the pH.

Natural, pure limestone cuts relatively easily with an angle grinder, bolster and mallet, or at the worst case a wood hand saw which you really don't want to use again or that needed sharpening anyway If you can cut the blocks, try to maximise the surface area of the finished shape.

I had 20 kg shell grit and 15 kg of calciam carbonate in my grow beds and it did f all i still had to use lime

+1


As this is a common problem perhaps we should be less dogmatic in recommending it as a solution to low pH

I agree. Only recommend Calcium Hydroxide, that is only after checking the water alkalinity first. 85-120ppm of Carbonates.

And don't check ph just after you add the calcium. It will read off the scale (high) untill it has all properly dissolved..

SuperVeg- Can you provide an approx time to wait?

2 hours....

I just wait till all the murkiness of the lime is gone. I just go inside and forget about it, then come back later. Usually to find the ph about the same as before, or only slightly less acidic