the first time I started my planted tank , I used the dirt technique.. all the plants grew out fine but as time went by (close to a month) I started seeing buildup with anaerobic spots (you can see mounds on the substrate) . and since this tank was in my room , everytime a bubble erupted it smelled like rotten eggs..

long story short. just make sure you do it right the first time for dirted tanks , dont hop through the procedures or youll tear down the tank like I did.

I prefer using ada soil (although its expensive) to plant, its just way easier to mess with. gives a good yr or so before nutrients are gone then you can use root tabs after

No reason dirt should not produce food for plant's throughout it's life assuming fishes are being fed and fishes are producing waste.
That food and waste which is not caught in filter's, fall's to the bottom and mixes with substrate ,and is then used by plant's each day that the tank is running.
In addition to the fish food and fish waste,one can add fertilizer's to the substrate and or water column.
With regard's to depth of soil and anaerobic condition's,the plant's transport oxygen to their root's which negates oxygen poor environment that is needed before anaerobic condition's are realized and even then,,the hydrogen sulfide is almost instantly rendered harmless once it makes contact with oxygen in the water.
Must be this way or those running deep sand bed's in marine tank's would report issues with the depth of the sand ,and they don't.
I do agree that if you are one who constantly or regularly uproot's plant's, that soil based tank's can make a right mess with regard's to water clarity, but with a little forethought,planning, with regard's to plant placement it is largely a non issue or can/should be.
Research the plant's you intend to use and info can be found as to where in the tank they should be placed, and you won't have to move em as much.
Been running soil based tank's for a few year's now and at depth's of nearly five inches to accommodate large sword plant's or crypt's without issues with fishes/shrimp's.
I mix cat litter ,peat,with the soil and cap it with sand or product such as Black Diamond blasting media.
The cat litter(plain unscented) has good cation exchange capabilitiy (CEC), and the peat does also, while softening my water a bit to suit the tetra's I keep which seem to do better with softer water.
Plenty of folk's run soil based tanks that use plain old top soil or Miracle grow organic choice .
As mentioned,,just need to do a bit of planning so you ain't uprooting plant's weekly which does nothing to help them growth wise and can make unnecessary mess.IMHO

Are you trying to create an aquascape or are you just putting plants in and want to enjoy the ecology of it all?

If the former is true, and I think it is because you mentioned ‘scaping’ I would stay away from dirt. As you suspected it doesn’t like being disturbed or played with.

If you’re new to this I would not use ADA Aquasoil (AS) either, although it’s great at what it does and I actually think it’s the “Substrate for Dummies” because it houses pretty much everything the plants need for probably a year or so (In other words, if you don’t dose enough of something the AS should cover your mistakes) but it takes an experienced hand to play around in AS, (Doable but again I think a newbie might get into trouble.) because it contains a lot of ammonia which will cause serious problems if not removed.

You can carpet pretty much with any substrate as long as you’re dosing the water column. If you want a dark substrate I would definitely recommend Eco-Complete. Although it’s far from ‘complete’ it’s very easy to plant in and much for forgiving when it’s disturbed. If you go into a typical pet store they’ll tell you Flourish Comprehensive is a complete fertilizer. That might be true in a low-tech setup where fish and waste provide NPK, but not in a high tech setup that has good light, co2, etc. You could look at Eco the same way. Not complete for high tech.

If you want a lighter substrate and want to save money use power-filter sand. About $7 for 50lbs. Good grain-size, tan in color and easy to plant in. Works fine as long as you’re dosing and providing good co2.

Every substrate becomes inert after awhile. I would go with black diamond blasting sand and root tabs. Even if you have to poke a hole in your carpet to replace root tabs every few months, they are not large holes. You only need one every several inches too (in a grid). Doesn't seem like a big deal to me in the long run. You could even poke the O+ tabs themselves through the carpet in a finer pattern. The capsules are only there so the O+ doesn't break down as you place it into the substrate. With a 75g tank, I don't think the minor deterioration of the O+ will be a big deal. I have had no issues with O+ bits resurfacing in my 75g and throwing off parameters. I'm not one for expensive substrates. My swords, crypts and sag have all grown fine in inert substrate with root tabs. I haven't replaced my tabs in 6 months and the growth seems fine.

As for the light, I think people tend to exaggerate the light needed. With medium light, which the Ray2 should give you no problem, and CO2, which you have, you won't have any issues. You should be able to grow just about anything. The 18" front to back may be a little too much for a single light. If you want a secondary fixture, I suggest a planted+ 24/7. The automatic sunrise/sunset would be nice and it would definitely push you into medium-high lighting. It would help with a more even lighting and give you some more colors than the Ray2.

Just another opinion.

Can you please elaborate on what you mean by "do it right?"

Bump: It's funny that you mentioned just pushing tabs through the carpet. Maybe you're right and it's not a big deal.

I'm really grateful to be getting so much feedback. It definitely makes me more comfortable in making a good decision because everyone seems to use different methods and they all work fairly well for them...I presume...or they wouldn't be recommending it.

Now, I am going for a nature aquascape. I want hills, and therefore a substrate that is going to work with me on that. I was planning on filling tupperware with gravel as a base to help with that, but I'd like a substrate that will hold it's position as well as possible.

Honestly I've dropped a descent amount of money into this already, so saving some money on substrate that I can spend on more plants and, if necessary, fertilizer would be a huge plus for me.

How does black diamond blasting sand hold up for scaping?

If I were to use MGO, what cap would be best for holding hills?

I am trying to aquascape, yes. Mostly rock hardscape. I'm playing with the idea of adding an area of sand, maybe to appear as a path, possibly even to a beach area. Most of the plants I think I'm going to be going with have fairly fine and short roots. Either a monte carlo or DHG carpet, moss of some sort to glue to the rocks, maybe some wisteria and others which do not grow very tall. I've honestly been very neglectful of the plant part, because I wanted to get my lighting, co2, and substrate all figured out first. In hind sight I'm realizing I should have figured out the plant part first. LOL. However in my defense I did know I needed at least a medium high light on DHG, etc so I THINK I took at lease a descent start in lighting on that regard.

Anyway, if I (hypothetically) were to use short and narrow rooted plants, would you still deter me from using MGO for scaping?

I have tried just about everything at this point and they all work. Some are just easier than the next. I have found potting soil and mineralized top soil work well but I use way less than most. I have had a few tanks go anerobic so I use an inch of either most. Capped with black sand or gravel and it works fine. Often, I just did 1/2 inch which didn't give me much of a cloudy result when changing things but I set all my soil tanks up where I wasn't rescaping a lot because it can get bad. The major upside of this is it's really easy to plant, the downside is major if it goes anerobic, for me, that is a tear down.

Flourite and similar has worked fine for me as well. Have had great success and it looks good if you pick a color you like. You will need to fertilize more than soil but in a high tech tank, it likely will end up being about the same anyway. On a low tech, soil may be a bit easier, or less maintenance but this is an easy combo.

My choice now is Aqua Soil. It has most the advantages of all the substrates I like without being a hassle. Mine has never broken down or become problematic and it looks good. It may seem expensive but you get more per bag so the cost isn't that much more than Flourite.

Root tabs may seem cheap and easy but if you buy root tabs, they really will add up over time. Other things like Osmocote or similar are used but then you end up with it your substrate so it's hard to reuse. Flourite can last pretty much forever so adding things to it with whatever DIY root tabs have in them, you may not choose to reuse it. Aqua Soil will eventually break down.

What is really cheap in the long run is dry ferts and that should really do more than any substrate will, especially in a high tech tank. Well, low tech tanks will benefit to ferts to but it will be less of a routine no matter how you go.

I am very much into experimenting and saving money but I wouldn't save money and experiment just because you don't want to spend money on something you actually want if you have something in mind because you likely will end up swapping it out later or using what you really wanted to next time when some substrate lasts forever. Lastly, like some said, many substrates are not nutrient rich but have a high CEC so keep that in mind.

A well thought out plan will go further than substarte choices, I have had pretty great tanks with gravel and pretty miserable tanks with Aqua Soil or potting soil.

I use ADA AS because I can scape a lot with it, it is all 100% the same stuff, so when I re slope the tank, the design etc, it does not look tacky and mixed.
It has a lot of ferts in it. Might as well use both locations for ferts.

No good reason not too really.

Takes some getting use to, newbies can run into trouble there and with dirt/sand cap mixes.

Go with sand based on your goals though.
Later, consider something else.

I value plantbrain's opinion very highly. Tom is a very respected member of the community and has been for a long time.

On the topic of hills, try some light diffuser/egg crate instead of the bowl idea. You can cut it and use it to help with hills. The best thing for a hill is roots though. So maybe try a dry start? That may help. It will get your plants growing a deep root system without washing away the sand. Then the roots hold the hill together. Just a thought. I've never done it myself, but I've read many journals of fellows doing it.

Who's Tom? some random guy?

sorry to derail, carry on...

He's just a knowledgeable member of the community. I found one of his tanks. (edit: Not sure if you were jesting!)

1500 g tank:

It's not a matter of what plantbrain uses or any other member here. You can grow a lush tank with all of them, but at the same time they all have their +/-. This is about what's good for a person who is new to this.

I use AS in almost all my setups, but for a newbie it could make things difficult if your not used to it. There are posts after post showing peoples tanks and how they can't clear them up, have massive issues because they stirred up the AS. There's ways around that, but again we're talking a newbie.

If you have proper lighting, co2 any substrate will allow you to grow plants.

Wow. How did you achieve that wall in the center of the back?
ETA: Just realized that's Tom's.

This is true. There is a sticky at the top of the page with a quick run down of pros and cons of typical substrates. If you can grow plants in blasting sand (completely inert), you can grow plants in anything. Plants are quite adaptive to their environment.

Plaintbrain has always had good suggestions from my experience with him. That's all my comment was pointing out. If anyone is seeking advice, which the OP was, I would point them to a veteran member of the community.

That's fine, it's all good.

Point I was making was if someone for example was new to keeping fish and they wanted to make zebra plecos their 1st fish, I still wouldn't recommend them even if he got advise from someone experienced with those fish. When your working with a substrate and are new to it, it's not the same as someone who has experience with it.