Six accounts of murder...

This is a question regarding PPM and top-offs:

Vegetative Setup
T5 Fluorescent
Drip Irrigation
18 Gallon Reservoir
18/6 Light Cycle
10 min. Feeds 3x Daily

Lets say I start off with PPM of 550; after 1 week it goes up to 800. I know to bring it down you simply add water. This is a "top-off," correct? How would I measure the amount of nutrients it needs? Will there be a time when the PPM goes down? Finally, as the plant grows it will need more nutrients per top off? Is there a set system for doing this or does it vary from strain to strain. Basically, is it something I will just have to experiment to find a good amount?

I have done quite a bit of reading on my own time and know the frustrations of people asking for handouts. This is one thing I couldn't find...

As you may have guessed this is my first time...Well, it will be my first time with all the information. My first attempt resulted in the massacre of 6 innocent Satori seeds...:(

Any information at all will be taken with gratitude as I hope to get the second attempt underway with all the info I need.


Herb, Freedom, and Power of Thought.

-Colour:rastasmoke:

Six Counts** of Murder...

I actually really like the title- it's why I opened the thread.

That's about it- you add water to lower EC/PPM ( see footnote) and add nute to raise it. If the plants are drinking more than they're eating, ya give them more water. If they're eating more than they're drinking, ya give them more food.

It's just about impossibly complicated to determine the relative ratios of nutrients in your solution- Large scale hydro produce ( lettuce, basil, tomatos) will either have a lab on site or, more commonly, sub out their weekly testing to a lab that serves a pretty good region.

The common practice is to maintain a consistant EC/PPM and replace the nutrient solution perioically. The larger your (res volume)/biomass ratio is, the slower nute ratios will drift, and therefore the longer you can go between complete changes. IE- you might get away with 14 days w/ 12 6"plants, but you'd need to go once a week for 12 12" plants, given a res volume of X.

If I saw little variance in periodic ( maybe daily?) EC/PPM measurements, I'd feel more comfortable going longer periods. If the EC/PPM was slamming around, I'd wanna swap out more often. Yer gonna have to see what ya see. 18g will bounce around a good bit once they get going.

If yer flying without a meter, then it's usually safest to use straight water or maybe a 25% mix, and swap nute more often.
If you're doing a lot of topping off, get a meter- it'll pay for itself in nute in six months.

Hey, it just occurred to me- you say " drip irrigation"- is the excess going back into the res, or just going to waste? If yer just going to waste, ya just mix according to label and set your timer to give at least 10% waste- IE, an 18 gallon res should end up with at least 1.8 gallons of waste draining from the media. 25 to 30% would be safer. Ya go thru a shitload of nutrient, but ya don't have to deal with any of this adjustment crap- you're just flushing the used shit down the drain. Even at 25%, I'd run a couple of cycles of just water through at res re-fill.

Hope this helped.

Footnote- "ppm" meters actually measure the electrical conductivity( EC) of a solution, which is then expressed in millisiemens (mS). A chip on the "ppm" meter then determines what the concentration of total dissolved salt ( TDS) would produce the same conductivity ( EC) and expresses it in parts salt per million parts water (PPM) and displays that number. As things which are not sodium chloride will have differant conductivities than salt, it's a pretty relative number.

Further complicating matters, theres debate about what the correct scale is- an EC of 1.0 mS can be expressed as either 500 ppm or 700 ppm, depending on who made the chip. It doesn't matter, as long as you know which one you have, and which one anybody that you're comparing notes with has.

Also, you'll sometimes see things expressed in conductivity factor, which is just EC(in mS) x 10. I guess that they just thought that decimal points were too expensive to print.

You see stuff in EC more and more often- I really prefer it to the ppm convention, if only because ya don't have to worry about the whole 500/700 conversion thing.

An objective response...and a shit ton of information! I really appreciate it. As for the meter I will definitely be going PPM/EC. Im quite sure that played a role in my first failure, alongside a PH tester. Do you recommend going with a larger res? Oh, and the waste is draining back into the res.

I was going to say that too rhizome....:D

As far as rez size goes....it's completely up to you and how much work you are willing to do to keep things in balance. Smaller rez, more monitoring of numbers and more rez changes, more nutes etc etc...(ps...I love it when rhizome says things like "biomass ratio") As long as you keep your share of it in order the plants don't really care. ;)
As Rhizome said....the ratios are important to keep in balance. It doesn't take long at all for numbers....while looking similar to you.....look very different to your plants and we all know it's not about you.....it's about the plants. :D

Nah- it's all about the bioassay...:jointsmile:

AMEN!!