Iwould suggest that a lot of defficiencies that look like nutrient defficiencies are actually CO2 defficiencies.
I don't mean that the ppm at DC is not good but the circulation can cause problems
I tried the PPS Pro a long time ago when my CO2 wasn't really up to scratch and went from regime to regime. It didn't work at that time but can openly admit that was more than likely due to the CO2 than the regime.
I currently use the EI method and will more than likely stay with it. I get a minute amount of GSA on 5% or less of my Anubias leaves that have another leaf very close above it so I don't think GSA can be attributed to EI
. My main reason for sticking with EI these days since I got circulation and CO2 under control is that for me a 50% water change is much better than testing with hobby kits I don't trust!!! I don't intend on spending lots of money on quality test kits when EI is working.
A note to add to Jason's observations:
Whilst light is accepted as being the driver for growth the role of CO2 is often ignored where I think the two work hand in hand with the latter being the much more important. When reducing to 15ppm 24/7 then the growth is less than running 30ppm 24/7. Therefore less nutrients are required. Although many people reading my posts would think I am saying that light above 2WPG is 'silly' that isn't the case. I mean to say that it is unnecessary especially for the beginner or someone who hasn't got their CO2 circulation sorted out to near perfection
So under any light what the plants need is not 'high' CO2 but adequate and stable CO2. This can be at whatever level chosen but must remain pretty much at a stable level. Then the plants don't have to stop to adapt to a changing level and the algae doesn't step in.
Therefore I think we can use CO2 as a limiter without algae issues BUT this would mean we need to be pretty sure that our 'system' has the capability to make sure that a lower ppm at measured area (DC) does not let other areas reach 0 or move up or down all the time.
Personally I think high CO2 (30ppm average will mean closer to 100ppm at source) is an excess just as EI is dosing excess. The plants may not be growing faster under a very high injection than they would under a stable lower level but with it being an excess is it more 'forgiving' for people who haven't got the setup perfect and therefore areas that may be unstable within the tank may still be at an 'adequate' level under a high injection and excess in other areas whereas under lower injection these areas may be under an 'adequate' level. If this lower level is at an 'adequate' level in all areas this would of course mean less nutrient needed
Room for error therefore just like with EI.
My injection is high at above 30ppm run on solenoid (near yellow DCs) and I have a heavily stocked tank (33USG with 28 Rasboras, 6Corys, 2 Otos and uncountable amounts of shrimp (nearly 2"/USG + shrimp) but I keep it that way because I see no problems with the fish. However I do have very high turnover and a good water turbulence.
I should add that this was under what is considered 'low light' of 0.9 - 1.4WPG of T5HO so people will argue this is the factor. This is a different argument. lol I currently use 1.2WPG (max) of high power LEDs and Parwise this will be much higher than 'lowlight' which again is another argument
By max I mean the whole 1.2WPG is only used for the central 4 hours with the lighting staggering from 0.2WPG for the first hour to the max at 2½hours and then max for 4 hours before repeating the cycle in the opposite direction for the final 2½hours (total 9 hours photoperiod.) This means that although the PAR is very heavy at full lights the photoperiod being so small and staggering up and down through the cycle reduces the 'total' lighting and may push it back down to the 'lowlight' bracket. This tank only has slow growers in it (Anubias/Ferns/Crypts) and therefore should be susceptible to algae. It never has fast growers in even at startup without any algae issues
I guess its one of the trade offs really but I wouldn't suggest lean dosing/PPS to anyone who has highlight without high water turnover and good circulation as I think using the 15ppm (non excess) is what causes problems in these cases.
Interesting read of people's experiences. Good thread
AC