Learn Turkish: Aldığımız akvaryum büyükçe. - The aquarium that we bought is quite large.

This is the adjective softening suffix! When added to an adjective, -ce or -çe means "quite", "rather", or "-ish". So büyükçe means "quite large" or "largish". It takes the extreme edge off the base adjective büyük.

Why did we use -çe instead of -ce on büyük?

Because of consonant mutation (often called the Fıstıkçı Şahap rule). The word büyük ends in the voiceless consonant k, which forces the following c in the suffix to harden into ç. Then, A-type vowel harmony gives us the e instead of a because the last vowel in büyük is a front vowel (ü).

How does aldığımız translate to "that we bought"?

This is an object relative clause. It is built from the verb almak (to buy or take). We add the participle suffix -dık to create the meaning of "that... bought", followed by the possessive ending -ımız (our). Because -ımız starts with a vowel, the k in -dık softens to a ğ.

Why doesn't the sentence end with a "to be" suffix like -dir?