I have several tanks that are exposed to either the morning or evening sun, and ALL are "infected" with algae. If you can control algae just by using large/dense plants, I am very sure many others will be keen to learn from your experience.
In any case, not all algae is bad, although most types make the tank look ugly and untidy. In fact, I have seen one LFS purposely and effectively cultivate "common" algae as decoration in conjunction with plants. *sigh* I have never been able to achieve the same effect. Nevertheless, algae (particularly film algae and green water algae) make excellent food for young fries.
One of the worst algae to get that is near to impossible to eradicate is the hair algae, of which the most infamous is the BBA (Black Beard Algae). Very few fishes will eat BBA. Anyway, all types of hair will get entangle to virtually everything in the tank --plants, decoration, sand, glass....-- even algae-resistant plants such as hornworts! The only solution appears to be to throw away all plants and water, thoroughly clean and sterilise the tank, decorations, sand and other static objects. Fortunately fishes are spared from algae "infection".
Summary:
Direct sun => guaranteed algae, unless you are using UV light to kill the algae spores.
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