How to get a tortoise to eat calcium -

How To Get A Tortoise To Eat Calcium [Easy]

If you have a tortoise then you’re probably aware that they need a lot of calcium in their diet to lead a healthy life. Their shell demands much more calcium than most animals need. But how can tortoise keepers be sure that their pets are getting enough?

How do you get a tortoise to eat calcium? The easiest way to get a tortoise to eat calcium is to provide plenty of calcium-rich foods and add some calcium supplements to their diet. While these supplements don’t taste great for tortoises, they ensure that your tortoise gets enough calcium.

So, let’s take a look at calcium, why they need it, why getting it from their diet is challenging, what kind of supplements they need for calcium. and then let’s briefly touch on the role of vitamin D3 in making sure your tortoise has enough calcium too.

Why Do Tortoises Need Calcium?

Calcium is one of the most essential minerals for tortoises it helps them to maintain healthy skeletal growth, to keep their shells hard and intact. Calcium also plays other roles in their overall biological systems such as promoting the development of a healthy nervous system.

A deficiency of calcium can cause serious issues for a tortoise and the most common outcome is a condition known as metabolic bone disorder which involves the softening of the shell, breaking bones and possible paralysis too. If left untreated metabolic bone disorder is usually fatal and the death is particularly unpleasant.

Tortoises can suffer from an effective deficiency of calcium in three ways:

  1. There is not enough calcium in their food.
  2. There is enough calcium in their food but there is also too much phosphorus. Phosphorus prevents the tortoise from absorbing calcium efficiently from edible material.
  3. The tortoise is lacking in vitamin D3. The tortoise may have enough calcium in their diet but without an adequate source of vitamin D3, their body cannot utilize the calcium in the diet and thus, they still present symptoms of deficiency.

Getting pet tortoises the right balance of calcium in their diets is something of a challenge and it’s one of the most difficult things about owning these reptiles.

How Do Tortoises Get Calcium In The Wild?

A wild tortoise clearly does not need calcium supplements because if they did, there wouldn’t be any wild tortoises. They get their calcium from their diet and they do it by consuming vegetation which is rich in the mineral.

The plants get their calcium from calcium rich soil. So, you will find that most tortoise habitats in nature are on or near calcium rich soil.

They may also give themselves a little extra calcium by eating some of the soil (or possibly, sand) when they are feeding. If the tortoise’s body signals that there is a calcium shortage going on – the tortoise will seek out a major source of calcium (this might be something like a discarded snail shell or a bone that has been fully bleached in the sun).

Yes, even in the middle of a desert you will find plenty of snails, so no matter where the tortoise is from – there is likely to be a very easy to find source of calcium. In fact, snails are such a good source of calcium that tortoises are regularly seen scoffing them down in the wild.

Can A Pet Tortoise Get Calcium Like This?

Unfortunately, this approach is much harder to achieve with a pet tortoise than it is in the wild. Not every home or garden has an endless supply of snails to leave around as snacks and more importantly much of the captive tortoise’s diet is high in phosphorous and not in calcium.

Unfortunately, many home tortoise keepers seem to be unaware that their tortoises need a calcium rich diet and they feed their tortoises on fruit and salad. While these things are fine, in small quantities, they aren’t supposed to make up the main part of a tortoise’s diet.

The Highly Selective Dietary Approach To Get A Tortoise To Eat Calcium

Now, the problem isn’t as easy to fix by tampering with the tortoise’s diet as it might first appear. OK, the tortoise doesn’t need as much salad and fruit and does need more dark greens in its diet but will making this change immediately make things better for your tortoise?

Related article: Is your tortoise a picky eater? Here’s what to do

While you will almost certainly resolve the calcium to phosphorus imbalance, you are just as likely to introduce another problem by accident. Chard, collard greens, kale, cabbage, spinach, etc. all contain other ingredients that can prevent the tortoise from effectively absorbing calcium.

So, the dietary approach almost always ends up with the tortoise being stuffed with “anti-nutrients” such as phytic acid or oxalic acid, instead.

So, if you want to correct the tortoise’s calcium intake via diet alone – you need to run a full chemical analysis on everything it eats to check for calcium content, phosphorus content and anti-nutrient content. This is very impractical.

Why do you think tortoises eat snails in the wild? It turns out that balancing a tortoise’s diet for calcium is too challenging for you and it’s too challenging for tortoises.

Do Tortoises Need Calcium Supplements Or Calcium Powder?

So, it should, by now, be fairly obvious that tortoises need some sort of additional source of calcium in their diets. Fortunately, there is a wide-range of both powders and supplements out there that you can give your tortoise.

However, it’s worth noting that not all these supplements are created equal and some of them can be problematic too.

About Calcium Supplements For Tortoises

There are a lot of different calcium supplements available on the market. That’s not an exaggeration. There are more than a dozen preparations that are commonly sold for supplemental use and they come in hundreds and, possibly thousands of different formulations.

The most common of them all is calcium carbonate. In your home, that’s limescale and it gives water hardness. It’s considered to be good for human health though and it’s supposed to help protect your heart.

Other compounds that you might see could include: bone meal, oyster shell, calcium gluconate, calcium lactate, calcium citrate-malate, dicalcium phosphate, and tricalcium phosphate.

They are not, however, all equal and not all of them are designed for tortoise diets. Calcium carbonate carries a huge amount of calcium by weight – nearly 40% of the compound is calcium. Calcium phosphate, on the other hand, carries a lot of phosphorous and only 8% calcium!

Unfortunately, calcium carbonate doesn’t dissolve and often if you need to put calcium in solution, you’d opt for calcium citrate which may only have half as much calcium but will easily dissolve in room temperature water.

Many other preparations include ingredients that you definitely don’t want your tortoise snacking on and you might find arsenic, cadmium, mercury, lead or aluminum in them.

Can An Excess Of Calcium Harm A Tortoise?

This isn’t completely understood. We know that an excess of calcium in human diets can cause problems, for example, the most common consequence was thought to be the fairly unpleasant condition called kidney stones.

Recent research shows that this might not be true, in fact, the reverse may be true, and a lack of calcium might cause kidney stones. However, it’s certain that a condition called hypervitaminosis-D is caused by too much calcium in human beings.

In tortoises there have been no symptoms noted or observed with very high calcium diets. However, to the best of our knowledge there has not been any academic study on the effects of too much calcium in a tortoise’s diet.

What Is The Best Routine Calcium Supplement For Tortoises?

Calcium carbonate is the top choice of supplement for a tortoise. Why? Well firstly, it is really cheap if you buy large quantities from an agricultural feed merchant. If you know that you’re going to need to supplement your tortoise’s diet – you might as well keep the costs down.

Secondly, it’s entirely safe and effective both with tortoises and, as importantly, with humans.

It should be ground to a powder (and ideally, it will be supplied that way) and then lightly dusted over the tortoise’s food. Don’t go mad with this, the taste is, apparently, quite bitter for tortoises and they won’t eat it if you put too much on.

If there should, somehow, be a shortage of limestone powder on the market – you can always grind down some calcium supplement tablets designed for human consumption. Though be warned they contain vitamin D2 not vitamin D3, so don’t think you’re also tackling a vitamin D3 deficiency like this.

What’s Wrong With Bone Meal Supplements?

It’s true that bone meal is an excellent source of calcium, unfortunately, it is also an excellent source of phosphorus. While you would increase their dietary intake of calcium by feeding the tortoise bone meal supplements – they wouldn’t be able to absorb it effectively.

In fact, as most tortoises have too much phosphorus in their diet already, you might make any calcium deficiency they have worse by using bone meal.

What’s Wrong With Egg Shells?

While egg shells are full of calcium, they also contain hormones (which may not be good for reptiles), they might have antibiotic traces left in them and worse, they might introduce salmonella to your tortoises and they are especially prone to carrying salmonella in the first place.

However, if you want to buy calcium supplements extracted from eggshells that are meant for human consumption, they should be absent these problems. They’re also going to be much more expensive that calcium carbonate.

If you grind down your own eggshells, on the other hand, you’re gambling with your tortoise’s health.

What’s Wrong With Cuttlefish Bones?

Cuttlefish bone is a good source of both calcium carbonate and calcium phosphate, it also contains a bunch of other elements that might be beneficial to your tortoise’s diet.

Unfortunately, while these are regularly used as a calcium substitute by tortoise owners, they aren’t absorbed well in the alimentary canal. You can add cuttlefish bone as a little extra calcium, but it shouldn’t be the primary source for your tortoise.

What’s Wrong With Turtle Blocks?

Turtle blocks are often sold in pet stores. What they are is Plaster of Paris which is a calcium sulfate chemical with some calcium carbonate in the mix. More than half of the calcium in these blocks has zero bioavailability. That means that they’re going to eat a lot and get little in their bodies.

It’s also possible that the heavy metal gypsum is found in Plaster of Paris and that might make your tortoise sick. There are other cheaper and more effective ways to do supplement your tortoise’s diet without the risks.

Our Preferred Calcium Supplement For Tortoises

So, as we said a little earlier, a calcium carbonate powder is the best recommendation. This should have no added phosphorous and if you’d like to give your tortoise a bit of an extra chance to process the calcium – it’s fine to get a powder with a vitamin D3 supplement added to it.

Why Vitamin D3 Matters For Tortoises (And Their Calcium)

Yes, vitamin D3 is important to the tortoise’s ability to affix calcium from the diet into bones, nerves, the shell, etc. so, if the tortoise isn’t getting enough vitamin D3, they’re going to show the same symptoms as though they were calcium deficient. Even though they might be getting enough calcium.

Do You Need Vitamin D3 Supplements Too?

If your tortoises can get 3-4 hours of sunlight every day, they shouldn’t need any vitamin D3 in their diets. Your tortoise will synthesize vitamin D3 in its body when it gets enough UV-B light from sunlight.

If your tortoise does not get this much sunlight, you should give them UV-B lighting in their environment and hopefully this will provide enough vitamin D3. However, if you feel that your tortoises are getting enough calcium but are still appearing to be vitamin deficient, it’s fine to add a vitamin D3 supplement to their feed.

There is no, current, evidence that suggests that too much vitamin D3 is an issue for tortoises.

What Other Minerals Help With Healthy Bone Development In Tortoises?

There are two other minerals that a tortoise needs in their diet in reasonable quantities to promote healthy bones: magnesium and phosphorous.


Oddly, magnesium helps the body to absorb calcium and, in particular, it appears to play a part in the production of hormones that regulate calcium in the metabolism. Tortoises will always get enough magnesium in their diet.


Yes, while too much phosphorous in their diets is problematic for tortoises, not enough would be a problem too. Given that nearly all vegetation has plenty of phosphorous content – you’re unlikely to have any problems getting enough phosphorous into your tortoise. The real problem is too much phosphorous.


There are other minerals that may/may not be important (our understanding is not entirely clear) including zinc, boron, strontium and manganese. However, given that these would only be required in trace quantity, it is very unlikely that your tortoise has a shortage of these minerals in their body or their diet.

If you have concerns that your tortoise’s diet is limited, you can give them a weekly general mineral supplement if you want to.


How to get a tortoise to eat calcium? Well, the best way is to add a light dusting of calcium powder to the tortoise’s food and to ensure that they are eating dark, leafy green vegetables which are also fairly rich in calcium. Calcium is essential to your tortoise’s health. Fortunately, supplements are cheap and easy to administer and there’s no reason that your tortoise should go without calcium at any time.

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