His water is pretty clear. I think he's changing a gallon every week, maybe every two. I'll suggest a nano skimmer. I don't know much about his setup, but flow is supposedly strong.
Does he have a test kit? Doesn't matter if the water is clear to the eye... you need to know what the parameters are. How long have the tanks been set up?
If you can please list the readings for both tanks for at least:
-Ammonia
-Nitrite
-Nitrate
-Ph
-Salinity
-Temperature
Also, what is the water source being used for the tanks? Is he mixing his own saltwater or buying it? Is he using tap water to mix with salt or reverse osmosis? The smaller the system the more important this becomes... heavy metals build up quickly in a small system.
The reason the everyone is against small tanks for beginners here is simply because the smaller the tank (the less water volume) the greater the effect is from any little change that takes place in the environment. Small tanks are totally doable but yes not recommended for beginners and require a lot more observation and work. For example just look at the numbers for evaporation alone. If you have 10 gallons of water and you have a half a gallon evaporate then that's 5% of the total water in the tank. On 50 gallons if 1 gallon evaporates that's twice as much evaporation and that's only 2% of the total water in the system.
And on these tanks (2.5 and 5 gallons)... once you add sand/gravel rock etc... you have even less actual water in the system. Sounds like he's not going to give up on them so you may be better off just trying to help like you are.
List the parameters if you can... yes he's better off choosing less livestock and hardier species but you want to find out what the real problem is before adding anything else to the tank and get it corrected first if everything is dying.
Please don't let him inadvertently murder a red scooter blenny. He shouldn't get that yet if he can't can't keep a clownfish. They are in the dragonette family and typically require live food to survive. You need an established system with pods etc and even if you have that in a small tank they will wipe out the population very quickly (like a week lol) and you'll be in a bad spot trying supplement live foods.
