29 gal, How many fish

Question
Hi Glenn,
You have helped me set up my 29 gal FOWLR aquarium and I have another question for you. Actually a 2 part question.
I added a pink damsel and 2 "nemo" clowns in my tank and all is well. They were in the same tank at the store when I bought them. People are telling me to get the damsel out, but I see no aggression at all. What's your opinion on that?
2. They are also telling me that with a 29 gallon tank, I could only put "maybe" one more fish in there and then some cleaner shrimp? That's all I can have, one more fish?
Thanks Glenn

Answer
Hey Joe,
Unfortunate fact... Marine life creates more waste. The rule of thumb for salt water aquaria, is 1 inch of fish per gallon of actual tank volume. So a 29 gallon, minus the rounding up of the industry(the actual volume of a 29 gallon is generally 28.3 gallons, the industry just rounds that up), the displacement of water volume for rock, substrate, etc... ends up being like a 23 to 25 gallon usually. And you base the number of fish you can keep based on their adult size potential. Now you can get away with a heavier load/bigger community, with more live rock, greater flow, deeper substrate, adding a sump, etc. But generally stick to the rule, especially with a new marine system. The Clowns will be between 3 and 5 inches depending on species, the Damsel will be between 2 and 4 inches depending on species. So add those up and you have a potential for 14 inches of adult fish. See where I'm going? You can safely add 2 more fish with a max growth of 5 inches each. Now you have to take into account the habits and activity of each species. Free swimmers? Sedentary or Active? They will need hiding/sleeping places and room to swim and explore. Happy fish with good habits = Long lived pets. Then your clean up crew, up to 4 shrimp, 6 small snails and 6 crabs. The snails if too large or too many, will starve or develop eating habits that take away from their cleaning duties.
The Damsels AND the Clowns can be extremely territorial and aggressive. Especially is a system that small. Even the Clowns can be aggressive towards each other if they arent a mated pair. They arent housed together for long periods at stores, so they never really develop a "home". In your system they will. Be prepared to separate or take someone back. They can kill each other through the stress, bullying, starvation(Ive seen clowns that wont let another eat). Just keep a close eye on them,  so no one suffers. They may very well just settle in together.