Goldfish dosent grow

[helptoall]

Hi, I have a 450L tank with 13 small to medium goldfish{ the biggest is 15 cm}. there are 2 external filters doing around 3200 L/H. Water P are 0,0,20 and were doing wc of 30% once a week. im feeding with JBL Novo Pearl.
all of the goldfish are rescued and some of them i have for around 3 years. it seems like when i bring a small new guy he often grows but then stops in a relative smal size. the 15 cm one i have for 3 years and he hasnt grow in the last 2 year..
what do you think is the reason? is it possible its some kind of health issue?

 

[PheonixKingZ]

@Deanasue ?

 

[Colin_T]

What are the tank dimensions (Length x width x height)?

You can try doing bigger water changes and feeding more, but 15cm (6 inches) is probably as big as the fish will get in that particular tank.

 

[helptoall]

160 on 40 on 70

 

[RobinS87]

you have to understand that goldfish also come in different sizes and I have a mini for example. In fact, they are no different from the usual, in addition, if you buy tiny, you will not even know it. The difference is actually that after 2 months they stop growing completely.

 

[helptoall]

you have to understand that goldfish also come in different sizes and I have a mini for example. In fact, they are no different from the usual, in addition, if you buy tiny, you will not even know it. The difference is actually that after 2 months they stop growing completely.

never heared of it.. do you hve any source supporting that?