Originally Posted by somewhatshocked
One month for Osmocote Plus and three for RootMedic? Even in super-heavily planted tanks that are high tech, I get a lot more mileage out of both.
Not to be a jerk... But I've actually extensively tested this. The membrane in osmocote allows nutrients to pass VERY quickly when fully submerged.
You might "feel" like you get more mileage... but you can't be. I mean, literally can't be. The nutrients are leaking out regardless of whether your plants are using them or not. If you have a high CEC substrate you might be hanging on to some of those nutrients, but they aren't inside the membrane any more.
If I could just use osmocote in my products, don't you think I would? Rather than have someone (the same company that make scott's products) make it for me for 3x the cost?
I've tested it more extensively than I care to admit. Even buried deep in substrate, the depletion rate is less than 5 weeks.
RootMedic's thicker membrane means that the ferts come out slower. If they are used up slower, they also do not escape as quickly during the initial phase as the nitrogen actually clogs the pores in thicker membrane. This is what helps the RootMedic membrane last longer in slower growing tanks. But eventually it would deplete even if no plants were present. It is the nature of a controlled rate membrane.
The "6 month" rating on Osmocote's bottle is for dry soil at about 75 degrees with watering every few days for just a few minutes. Now turn that into 75 degrees fully submersed...
If you want to test it yourself I bet you can see. Put it in a cup of water. Test for ammonia. Drain water, repeat. After less than a few weeks they'll have nothing left. This is a sped up version of the test, but representative none the less.