Hi, AdAndrews,
speaking as one who knows nothing, up until relatively recently, I've never used a nutrient substrate or ferts to keep plants going, merely inert gravel, but have always had live (and sometimes dead/dying) plants.
And I've never used co2 - and in previous decades, neither did cumulative millions of others.
It depends on what type of plants/tank you want to keep.
But, apart from those already mentioned by others, there are a number of issues potentially involved in the problems you've been having, including the fact that comercially grown plants may have been grown emergent so that leaves and stems developed in the air will initially die off under water (and hopefully regrow) and that crypts, for example, tend to melt when moved, and may or may not make an eventual recovery.
One thing I was wondering was, do you have very coarse gravel?
I have fair-sized polished quartz in one tank, and the only plants that really do well in there are crawler-types that aren't so much dependent on roots.
And it can take some time for these to really kick in and start doing well, unless ferts are used.
That tank's been running for a year, (possibly 2, get mixed, have 10 tanks and a bad memory) is established, and must have mulm underneath; I did put root tabs in, way back when, but they'll be long gone.
I've put in several plants which are potted (in soil under gravel) to compensate.
I ran out of Flourish, was told it wasn't available thoughout Western Canada for a while - plants started dying back, and even dying period, in several (non Walstad) tanks.
It makes a difference...
It's not unusual for critters to travel in on plants, some of them plant eaters which may attack (specifically or generally) roots/leaves/stems.
Many people use a dip and others also q-tank plants as well as fish for similar lengths of time, to catch any hatch-outs prior to their infecting the whole tank.
Some of these literal little blighters can destroy a whole tank of healthy plants (sniff) in a very short period indeed, once brought in, especially if several types are introduced..
As recommended by others above, especially in a new tank where mulm has not yet built up, ferts are a good idea, even if only used over the first months as a boost.
But if co2 is to be used, the increased rate of growth will, as you probably know, require a regular fert schedule.
Since your lighting system has been declared to be good enough, there may be multiple other factors at play, many dependent on circumstances having little or nothing to do with your tank environment.
A good dosing regime and co2 injection will undoubtedly overcome many of these, if only by the faster growth of surviving plants.
But if a high tech/high maintenance situation does not happen to be your preferred method, there may be other ways to achieve reasonable plant growth.
The 2-4 week period mentioned prior to plant death makes me wonder about the softness of your water.
In this case, it sounds most like a mineral deficiency - and (speaking as One Who Knows Nothing and has no money to spend on high-tech I know nothing of anyway) I'd try root tabs and a bit of Flourish (or whatever's similar in your area) for a water column fert - maybe a bit of calcium/potassium (edit - oops, missed magnesium somehow) deficiency?
Because deficiencies also can put holes in leaves, making a plant appear to be 'eaten' when it's really just falling apart from lack of nourishment.
In any event, best of luck.
Being the opposite of expert, I can only say what's worked for me, or what I've read that makes sense to me, in case anyone else might benefit.
I can sympathize because I've had problems with dying plants on a number of occasions, which is why I'm aware of the potential problems listed above.
And it sucks!
pippoodle - tank pics = WOW, how'd you get Amano to do your tank!!!
And what's the blue tornado-shaped thing on the far left?
His trademark?
/s411.photobucket.com/albums/pp200/AdAndrews/
/i290.photobucket.com/albums/ll251/O...rborSeal800.jpg
