Advices and opinion needed for my setup

[PNT Guy]

Advise or views needed for my 3ft by 1.5ft by 1.5ft tank...
If there is a need for upgrade or add ons

-It is filled up to around 160L
-matured cycled tank
-In it are one 7"pnt, two 1" Cichlids and one 0.5" corydoras.
-pH usually ranges from 7.85-8.29, hard water, ammonia 0ppm, nitrite 0ppm, nitrates 15ppm
-One internal filter with the outlet connected to a top filter filled up with oyster's shells, cc and lava rocks
-Two atman at3338 canister filter with the output of 1800L/hr max for each filter.
-Diet mainly on hikari turtle sticks.

-Every 15%/4days wc i treat the tap water with api stresscoat,
after letting it to age for at least day.And wc i add sodium bicarbonate,OF GH+, OF Himalayas natural pure crystal salt and add a little bioearth

Here is the pic of the canister set up....

Thanks for all the advices and opinion in advance cheers