James Silence

Jay Smithy wrote:Regarding "Rock Wool".
First, unless the package you get it in specifically states that it is something else, it is likely just cheap, course fiberglass insulation type material.

Rock wool and fiberglass are definitely not the same material. Just as the name already suggest, rock wool is made out of rock while fiberglass is glass. Neither one is cheap in terms of processing since both require the material to be molten and then spun into the actual wool. So energy wise both materials are expensive. For rock wool production stones are literally molten into lava using coke. A small stream of lava continuously exits the furnace where it hits a spinning disk. The lava spratzes solidify mid air and are taken up with an air stream and the fresh rock wool is then continuously processed into the size and densities required. The rock wool cubes are not waste material from insulation production.  

Jay Smithy wrote:
Second, unlike just about any other growning media, depending on grade, when you take plants out of rock wool, you tear the roots up and leave a lot of root matter in the stuff, where it will break down, which is not the wosrt thing I guess, but TERRIBLE if you are transplanting.
Removing plants from almost any other media turns out to be better, cleaner, easier.

This is why you don't take the plants out of the rock wool cubes. Why would you? Rock wool is an excellent material when using the seedlings in a hydroponic system. You transplant by simply dropping the cube into correctly sized brackets.
The material has a good capillarity and due to its nature and production process it is inert and sort of sterile. This allows you to condition and inoculate it in any fashion your plants need.

The only drawback is the non-recyclability of the material. I am not sure whether there are "usage after usage" concepts for this.

Tom Connolly wrote:I will be putting a 70 gallon (230 liter?) aquarium in my living room. I will slowly stock it with juvenille fish and let grow big together - major point us that the initial bioload will be low.  I would like to put two shelves over the aquarium and put 4 house plants on each shelf. They will most likely be spider plants and will also start out as clippings. They will all be grown hydroponically, without any soil.  I would like to circulate the water from the aquarium into the plants but I dont know how to calculate the balance so that the water is kept clean and the plants have enough nutrients. Any suggestions?

Dear Tom, buy an el cheapo EC-meter (roundabout 50-100$) and monitor your aquarium water. Keep EC (in mS / micro-Siemens) between 1.0 and 2.0. Below 1.0 your plants may start to starve. Above 2.0 your fish will start to suffer. Buy a cheap hand held pH-meter and keep your pH between 6.0 and 7.0. pH should slowly go down over time. Bring it back up with Calcium Carbonate (Marble, egshells) or Potassium Hydroxide (please be careful).

Buy nitrite "stickies", for example from Merck. Check weekly.

Don't panic when EC is too low or when pH goes below 6.0 or above 7.0. Simply engage in counter measures like water exchange or bringing the pH down.

Add a little bit of liquid iron chelate every now and then. It is available in small quantities in aquarium shops. But there it is very expensive. It becomes much more reasonably priced in larger quantities. I'm buying 30L for roundabout 100€.

In general: You can manage your system with an EC-meter and a pH-meter and some carful observation.