Adding multiple filters

Question
QUESTION: I have a 50 Gallon tank and these are fishes I have at present:
8 Small Cory Cats
6 Glowlight Tetra
5 Flame Tetra
4 Bloodfin Tetra
6 Cherry Barb
10 Harlequin Rasbora
There's one Internal Power Filter (sponge media) with max flow rate of 264 Gallons/hr & one Sponge Filter connected to the air pump.
Now I want to add about 20 more Neon or Cardinal Tetras over time and I am aware of the fact that the tank will probably be quite overstocked & the risk associated with it.
So my question is:
If I add another Top Filter with, say, Ceramic Ring media will it help in maintaining the water quality or will it just be an useless addition ? Technically, shouldn't adding an extra filter help in housing more beneficial bacteria ?

ANSWER: Hi Deep,

The good news is you have a decently large aquarium and groups of fish that produce a very low bioload and therefore have a low impact on the aquarium's biofilter system.  I feel adding 20 neons or cardinal tetras would be a fine addition to your current setup.

Sponge filters do wonders for providing a massive area for beneficial bacteria to thrive. I don't necessarily believe adding the ceramic ring media is entirely necessary. The most important thing you can do for your fish is keep up with regular water changes. The more the better!

Monitoring the nitrate level in the tank is a great way to get a good estimate on the pollution level in the tank. Ideally you should aim to keep it below 10ppm.

Adding some easy live plants (maybe you have already) are also great nitrate absorbers and your tetras, barbs and cories will greatly appreciate them. Java moss is an easy plant that is a great nitrate absorber as well. Java fern and water sprite are other species that are easy to care for.

What an awesome tank this will be with all those colorful interesting species and the school of neons or cardinals will be breathtaking!

I hope this helps and best of luck!
Susan~

---------- FOLLOW-UP ----------

QUESTION: Thank u so much Susan. Guess I won't spend money on another filter then.
I have another query....
A while back I asked u whether a dark substrate will help in enhancing the color of the fishes and on your advice I covered the white pebbles with a thin black gravel layer. It worked GREAT and the fishes look much better now..
Problem is, since the dark layer is quite thin and the black gravel is smaller in size than the underlying pebbles, everytime I try to do some redecorating that involves digging in the substrate or, more importantly, gravel vacuum the top black gravel tends to move down bringing up the bottom 'whites'. Now I can't add too much of the black gravel cause that will make the substrate too thick which, I've heard, is not recommended unless its a planted tank.
So, I was thinking, what if I take out the white pebbles completely leaving only the black gravel.. Let's say I change one small portion (about 5-10 % of the total surface area) at a time and give a few days gap before the next. Will doing this ensure the 'biological balance' is not broken while changing the substrate ? If not, is there any other way this can be done ?

Answer
Hi Deep! You're welcome!

Good thinking there about changing the substrate out little by little! That's exactly what I would have recommended. You'll be a lot happier with all dark gravel and not have to worry about mixing the old white pebbles anytime you gravel vacuum or arrange the tank. It definitely won't hurt to gradually swap out the old gravel for the new in the amounts and time span in between you mentioned. It should all work out perfectly fine. Taking out old gravel may be a little messy by stirring up trapped debris that may cloud your water but this should settle or be filtered out with time. A water change helps tremendous too!

Best wishes!
Susan~