Can I add rocks to an full tank?

[Lexiih36]

So my tank is nearly 2 years old. There are about 7 species of plants in my 20 gallon. I want to add some big rocks in here just to add some flair to the tank, but the tank is already filled with water and partially stocked with fish. Would adding 4 or 5 rocks to here and rearranging the plants in the tank be too much?

Bonus question, I don't love how this looks, any suggestions on how to make this tank look better?

 

[Colin_T]

Just do a water change and before you fill the tank, add the new rocks, then top it up. But gravel clean the substrate before putting the rocks in,

I would get rid of the pebbles and just have sand on the bottom.
No idea what the dark green stuff is on the front right.
Put a picture on the back of the tank.
Add some tall plants like Ambulia, Hygrophila polysperma or narrow Vallis along the back.
Not sure what the plant on the surface is but maybe swap it for Water Sprite or Red Root Floaters.

 

[jaylach]

You can add all the rocks you want you will just need to remove some water. Remove enough water to give working space then replace the water in the amount needed to refill the tank.

You will want to use neutral rocks such as slate or lava. Marble can also give some nice effects. Rocks bought at a fish store should be fine. If using rocks you find wash well, mayhaps even boil, bake or microwave to kill any possible bacteria and/or parasites. Don't use any rocks gotten from an area that may have had pesticides or fertilizers.

As to the bonus question... I'd cover the back of the tank with black paper and add some taller plants in the back. Also consider mounting the heater horizontal instead of vertical. Mount it low and it won't stick out. Also, since heat rises, you will get better dispersion with the heater mounted horizontal. At least I assume that the big black thing is a heater.

 

[Wills]

It sounds like you want to do a rescape and its very doable - lots of good advice above.

If you can simplify your equipment, get an external filter, move the filter to a corner, sand substrate and then add your rocks in. If you start with the hardscape first you can add the plants. You have a couple of hard to grow plants in there that look quite new, how are you finding the plant on the mesh at the front?

Wills