Backyard Aquaponics
A place to discuss aquaponics

The ph would stay high. Ideally you want the ph a little lower than the coral would buffer it to. Our SoCal water is already a little high on the ph, and I notice some of the effects of nutrient lockout because of it.

Yeah I think my tap is around 8.0 and I think crush coral buffers it to 8.2.

A few years ago i did an experiment 4 identical beds running the same water one 1/4 blue metal one 20 mm scoria one hydrotron and the last vemiculite planted each with the same plants and guess what they ran for a couple of years there was no noticeable growth difference in all the beds
The vemiculite one after 4 years showed signs of blocking

Thanks F&F, valuable information.

Food&Fish - Thanks so much for the information - I'll now go 20 mm scoria with peace of mind

After four years... That sounds reasonable to me. Cleaning vemiculite is not exactly back breaking. Did you notice any plants that would only grow in vemiculite? Carrots or the like?

I wouldnt fill the beds with scoria as its a pain to plant in. My beds have scoria in the bottom half and are topped with either 20mm pebbles or canna clay

+1. Though I recon my cheapness will get the better of me on my next grow bed and I will end up with all scoria again.

It is very hard to dig through past a certain depth, even. With a hand trowel or spade.

My blue metal is the same, PITA to plant in.

I love my mix of peagravel and hydroton, a real pleasure to plant in and even removing big root balls.

just thinking cost........

Id personally go the 14mm screenings in the link you provided.

I might do a top layer of those screenings - quite expensive.. scoria is like $50 per cubic meter, vs screenings about 110 per cubic meter..

VS clay balls @ $50 for 50litres (x about 10 bags)

Yea maybe do similar to what mantis has done and use scoria for the bottom layer and screenings on the top 150-200mm-ish.

I used to have 100% pea gravel in my GBs and found it very hard to work with, so I added a layer of expanded clay to make things a bit easier, which it was until the clay and the pea gravel started mixing whenever plants were ripped out. Luckily for me, some investments came good so when the time came for a new system, I could afford 100% expanded clay in my down-sized replacement project.

I'd like to say that I'd never go back to using "heavy" media such as blue metal, pea gravel etc, but I know for a future project still in the design phase, the cost of expanded clay will be prohibitive and I will probably revert to using 12mm pea gravel with just a few bags of expanded clay over the top because even when it does mix it is still easier to work than 100% gravel.

Expanded clay is luxurious in comparison to other media and recommended, if you can afford it, though at around $800/m3 it is VERY expensive compared to $126/m3 for 12mm pea gravel or $135/m3 for 10mm blue metal gravel.

What about seportaing, say scoria (bottom layer) and hydroton (top layer) with a layer of shade cloth or someting similar that wont break down or clog up over time. it will eliminate mixing layers. Anyone tried that?