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can you feed algae wafers to goldfish?
i mean, they do eat algae right?
Yes of course

algae wafers are popular additional food for goldfish. Just make sure ur buying the ones with "spirulina" listed as the first ingredient.
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and if you buy goldfish food that enhances colour, what does that mean?
does it mean the goldfish will just turn a brighter colour, or will it change colour, will turn bright orange or white, or black (i love black goldfish )or what?
do colour enhancing foods realy work & how do you prove it
This is a somewhat difficult question to answer. Colour enhancer foods usually means that it will deepen and make red more vivid, but sometimes it also will result in white areas becoming pink. There are also reports of blacks turning copperish.
I feed my fish Hikari Lionhead which is an aggressive growth and colour promoter. Some of the red & white fish has the red areas spreading but the blacks remain black.
I really don't know if the colour enhancer really works, but so far it has served me well.