Rockwool Slab Ebb and Flow System - Some Pointers Please

So I have bought 6 of the trays and slabs pictured below and am about to build a frame and set up a reservoir system.

However because there isn't that many folk that use these here I just wanted to check on a few things to make sure I have things straight.

Before I start incidentally just some background on why I have chosen this system are:
1) I live on the 4th floor of a building and hate carrying heavy waste down 4 flights
2) Seems this system would require very little maintenance with use of timers and occasional topping up and changing of resevoir
3) Final wastage after grow would be minimal with just the rockwool slabs that would need to be disposed of
4) Convenient layout for space.

Regarding layout I have opted for x2 600w HPS lamps, each hanging over 3 trays containing 8 plants ie 3 plants in end tray, 2 in center and 3 on end (better spacing then 3,3,3 or 2,2,2 I thought)

Now for some pointers please just to make sure i get things about right:

Indentley found a very useful site on this method, for those that are interested as it does seem super easy:
http://www.just4growers.com/stream/hydroponic-growing-techniques/growing-in-rockwool-tips-from-the-pros.aspx

OK so

1) I have opted for x2 15 min feeds per day, but will obviously gauge this amount as I go based on how soaked the rockwool is.
2) I will be growing from seedlings and transporting them to 6 inch blocks that will sit on the slabs
3) I am considering placing the slab on a inch layer of hydroton at base of tray to aid in root growth, air flow and drainage. This will mean the slab will sit slightly above the lip of the container but as drippers are being used this shouldn't be an issue. The bottom of the tray does have groves but they are very slight.
4) Change out nutes and reservoir according to daily top up of just water, until initial starting volume of reservoir has been reached. eg 2 gal top up per day in 60 gallon tank = change of reservoir water+nutes after 20 days.

So that's where I am at so far.

Some questions I have are:
- When should I move up from 1/4 nutes to 1/2, to 2/3 to full ?
- How far should the 600w HPS be from plants during veg, (I guess I mean when roots show on 6inch blocks)?
- In winter how do you best keep a room well vented and yet stop it from getting cold too fast?
- Is there a quick way of sexing the plants before roots start to poke out of a 6 inch rockwool blocks!!
- I have no idea what nutes to use with this set up so some advice would be great.
- Oh yes and finally what ppm nute level should I be aiming for with this set up?

Thanks guys.

Any reason in particular for the rockwool choice?
Some people like it, but it seems old school to me. To each his own. Hydroton IMHO is more forgiving, not that rockwool won't work though.

Forget the whole nutrient feeding paradigm. Use only so called base nutrients no supplements. I mix my own nutrients, but before that I used Jacks, and before that I used GH. Its up to you, but nutrients aren't something thats magical, so no need to pay a magical price. Start off at a low ppm, and if the plants are loving it keep it that way. If you see deficiencies up the ppm. Less is more.

In winter you don't intake air from outside.

- Jiji

jijiandfarmgang said:

Any reason in particular for the rockwool choice?
Forget the whole nutrient feeding paradigm. Use only so called base nutrients no supplements. I mix my own nutrients, but before that I used Jacks, and before that I used GH. Its up to you, but nutrients aren't something thats magical, so no need to pay a magical price. Start off at a low ppm, and if the plants are loving it keep it that way. If you see deficiencies up the ppm. Less is more.

In winter you don't intake air from outside.

- Jiji

Click to expand...

Yeah the main reason is minimal waste and effort, that and I've got a bad back so the timer can do most of the work in this set up!

Where do you buy base nutrients?

I take it you mean you make up your own combination of nitrogen, phosphorus and potassium? If so what mix of nutes and produced best results? And do you change the mix during late bloom?

Fertilizer supply store, cropking, mbferts.......

Kind of, but also micronutrients...my own recipe isn't really my own, just pretty much copying others and fiddling with them using hydrobuddy ever so slightly. I'm no expert and I don't think there is a best.

There's many differing opinions out there on whats better than others. I'm not into the whole pk boost thing, and give them more nitrogen than most in flower so the plant stays looking healthy.

You can get pre-made dry HYDRO-mixes (from places like J.R. Peters, there are a few companies that do this), just match the ratios to mj ratios. They are usually made to supplement with calcium nitrate (to adjust nitrogen and calcium levels), and get some epsom salts for magnesium. 100 bucks and you'll be set for years. Also make sure to seal everything in a dry container.

- Jiji

OK thanks. After all that saw some some Canadian xpress hydro nutes bought 10L or bloom and 10L of veg for £30 in total (about $40) ! Normal RRP of this much would have been £160

I use Rockwool and only Rockwool . Cheap and easy to work with . No odor and no bugs.
You can check out my signatures to see what I am doing.
You most certainly can place the 6" blocks on top of the slabs to give roots more room . I would recommend NOT to use hydroton under them . Not necessary. Just more cost and a pain to clean for re use . Make a smaller system for vegging the plants and after you are sure they are female , you can then move them to the slabs to flower. Remember , when it comes to feeding , less is better. Over feeding costs more and can burn plants. When fixing plant problems , look at the new growth. You can't fix the old damaged leaves .

There are quite a few ways to sex the plants before they get through the six inch blocks. Some plants show early in premature flowers, look closely at the nodes. Another way is to, as soon as you get the seedlings, take a cutting and put it in 12/12 light schedule or 8on/16off. Another way is to take a branch and cover it with an opaque bag for forty-eight hours, some say you only need twenty-four or seventy-two hours. You could be able to tell sex in ten days. I've heard of another way, but I haven't tried it. Blue light during dark period will induce flowering.

I was just thinking about sexing the plants and timing before I came on here to check on thread! How bizarre. I wanted to ask about timing using rockwool. How you go about cycling your grow room and getting the timing right for when vegging females start to poke through end of block?

Also thanks for the sexing tips Warble. Dadio161 can I ask how you've been getting on with just using rockwool. You using slabs? Tbh although I am new to this method it makes so much more sense. In fact I've read that many of the professional set ups use this method. Oh and thanks for helping me make up my mind not using hydroton. The initial thinking behind my thinking about that was because I was factoring in using 4'' blocks, didn't even know there were 6'' blocks out there. Those extra few inches should make all the difference and mean i needn't bother with the hydroton base now as you suggested.

Phar , I put my clones into 4" cubes and veg them until I am ready to flower . I use the 4" cubes because of limited room in my veg cabinet. When I am ready to flower , I set the 4" cubes on top of a 6" block. Set them right into the tray . No hydroton. Just set them in the plastic tray . Plenty of room for root system with a 4" on top of a 6" . There are pics of this in my signature. I have thought about using slabs one day but I just have never gotten around to it.

even better a 4'' on 6''. As much room as a pot then if not more!