It has been said many times on this thread but apparently it needs to be said again.
The key to fighting slime is biological diversity.
Diversity can 'choke out' the likely singular anaerobic bacteria that has turned your plant into a slime haven. If you can fight it off with 1,000... 10,000... 50,000+ diverse forms of life, you have a much better chance of ridding your rez from the grip of slime. Pure earthworm castings are one of the only available sources of such significant biological diversity. A very important biological for fighting slime is Trichoderma. A tea that is brewed to kill slime should include this, as well as sources of beneficial fungi and bacteria. Types of endo & ectomycorrhizae fungi should be included as well to help fortify plant roots, in addition to providing the many benefits that they do. We happen to like Ancient Forest around here, seen to many of us as the most diverse product on the market.
If you are not fighting slime, you do not need as much diversity.
Having basic colonies of living, aerobic microbes in your system will often prevent anaerobic conditions from occuring, as the good microbes gobble up the bad ones before they can totally infest. In addition to disease prevention, a living aerobic system also provides other benefits to your grow, including increased water uptake, increased nutrient uptake, better root and plant health, and increased root branching. Of course if your environment isn't good then nothing will prevent anaerobic conditions from occurring. Using products that contain beneficial bacteria and mycorrhizae fungi can help your system stay clean before an outbreak occurs, or after after an outbreak and inoculation take place.
Common INEXPENSIVE products recommended in this thread include:
Mycogrow Soluble (beneficial fungi [endo & ectomycorrhizae], beneficial bacteria, and trichoderma; ~$10);
Botanicare Aquashield (beneficial bacteria; ~$12);
Botanicare ZHO (beneficial fungi [endo & ectomycorrhizae] and trichoderma; ~$20);General Organics Ancient Forest (most diverse formula of beneficial fungi [endo & ectomycorrhizae], beneficial bacteria, and trichoderma; ~$14);
Other common products recommended but EXPENSIVE include:
General Hydroponics Sub-M (beneficial fungi [endo & ectomycorrhizae] and beneficial bacteria; ~$45);
General Hydroponics Sub-B (beneficial bacteria; ~$45);
Plant Success Great White (beneficial fungi [endo & ectomycorrhizae], beneficial bacteria, and trichoderma; ~$90);
There is one other product some people have success with, but it is controversial. It is largely an anaerobic bacteria in it's composition, and therefore, could very worsen a slime infection. Probably great for growth but a poor choice for slime control:
House & Garden Roots Excelurator (beneficial anaerobic bacteria; ~$60).
"a guy at the nursery says all he uses is tap water and kangaroots in his cloner and has never had slime" - because he has never had slime, the basic forms of life provided by kangaroots are enough, in combination with his environment, to keep the anaerobic slime bacterias from thriving. please note, however, that both the kangaroots and microbebrew products posted include types of beneficial mycorrhizae fungi, beneficial bacterias, and even some trichoderma, but in most cases, they lack the diversity (only a few dozen) and amount of microbes requried for slime fighting. you could increase the amount of microbes by brewing these products into a tea with some molasses, but this would not add to the diversity. that could only be achieved by starting with a more diverse product, like Ancient Forest (up to 80,000 types of diverse microbes), or another type of earthworm castings. as with any inoculation of biological products, they must be refreshed periodically as they lose diversity and life over time. having a rez full of dead microbes will quickly allow anaerobic microbes to eat them up, and create slime in the process.
Hope this helps,
mr.bond