What is Ash in aquarium fish food?

Ash or ‘crude ash’; we’ve all seen it listed as an ingredient in fish food. But what exactly is ash in fish food, and why do they put it there?

As marine biologists, we’re well placed to answer this for you.

Question: What is fish food ash?

Answer: it’s another word for minerals and it’s listed as a percentage of the total ingredients.

Right that’s the short answer out of the way. For those that just wanted to know what is was, you can stop there. For those more interested read on, as we’ll cover in more detail exactly what aquarium fish food ash is, what minerals it includes, how those minerals are derived, if it’s harmful for you fish, and why it’s there. There’s lots to cover and it’s pretty dense, so proceed with caution and only if you’re genuinely interested.

Introduction to fish food ash:

Fish food doesn’t have the same requirements as human food. While we may love our fish, they just aren’t going to complain as much as humans regarding nutritional labels. Human labelling is stringent-ish, and though we all know how much garbage is added to a lot of our food, there at least has to be documentation of what it is. Whereas ‘ash’ is a pretty broad term and doesn’t actually give any indication of what it really is. For example, ash could be what’s leftover from Sunday’s BBQ.

So we want to break down what ash in aquarium fish food is produced from, and then give our best analysis based on the research and chemical analysis testing we’ve done on common aquarium fish foods.

What is Aquarium fish food ash made from?

Ash in fish food is minerals. These are made up in varying proportions of magnesium, calcium and phosphorus. More ash in fish food constitutes a higher mineral content, however it’s not easy to tell what these portions are.

Usually the ash content in fish food will range from 5 to 15% – that’s quite a large difference. Ash is expressed as total dry matter, meaning that the specific quantities of minerals within the ash are not known unless chemical testing is performed. We only know the percentage mineral content as a portion of the total ingredients.

Since it’s not really important to know the mineral variations of your fish’s diet, it’s not something people care about other than simply finding out what fish food ash actually is.


How much Ash should fish food contain?

What is a good quality fish food?

A good quality fish food tends to have a lower percentage quantity of ash.

Is ash in fish food harmful to aquarium fish?

The short answer is no; ash in fish feed is not harmful to aquarium fish.

It’s a bit like asking if lots of wheat and cheese is bad for humans, well not really, but it’s not going to make you the healthiest person in the world either.

Fish aren’t hipsters, they’re not into keto or vegan diets, they don’t care what they’re fed. And it’s certainly not harmful for the fish. The question is really, is it the best thing to feed them? The answer to the latter is no, it’s not. There’s multiple reasons for that…

  • High fiber and ash content isn’t easily digested by fish. It’s for that reason alone, that there will be more fish waste which leads to increase water changes and filter cleans.
  • It’s not scientifically proven, but based on comments we’ve received and forums we’ve studied, we think the mineral content causes fish to eat more – almost like additives or flavor enhancers in human food. If this is the case, which we can’t back up; then more fish waste will be produced as well due to over eating.

However, if you’re looking for a premium food, then look for genuine protein sources and less ash content. Your fish will have a richer nutrient diet, and while they may not care – their colors will be more vibrant and the overall health of water quality will increase.

But Why is ash added to my fish food?

There’s really only one answer for this. It’s the cheapest way to get fish the minerals it would get naturally. However, it’s high percentage in fish food shows it’s there as a filler more than it is for the sake of the fish, these minerals are low quality, and cheap. Flake Fish food without ash, that is made up of whole organic ingredients would be costly.

Ash and aquariums: a conclusion

Well there we have it, aquarium ash isn’t as malicious as it sounds. We hope we’ve addressed what ash is in aquarium fish food. If you have any questions, please contact us or leave a comment below.