Calcium, Vitamin D & Phosphorus for your turtle

Importance of calcium

Like any other pets, red-eared slider requires a wide variety of vitamins and minerals to lead a healthy and happy life. When it comes to nutrients for turtle, Calcium is perhaps one of the most discussed topics, yet calcium deficiency is still one of the leading causes for most of the health problems for red-eared sliders.

A common misconception for pet owners is that as long as I give my red-eared slider enough Calcium, they will not be subjected to calcium deficiency which leads to metabolic bone disease.


Your turtle can have all the calcium in the world. But if he is unable to metabolize and make effective use of the calcium, it is essentially useless. In order for your turtle to have a balanced calcium diet, the following 3 criteria must be fulfilled :

  1. Adequate calcium intake
  2. Adequate Vitamin D3 intake
  3. Maintain Good Calcium to Phosphorus ratio.

If any of the 3 conditions are not met, your red-eared slider will have an elevated risk of metabolic bone diseases. We will explore all the various topics through the article. But first, let us look at what is Metabolic Bone Disease.

Calcium Deficiency in Turtles

Domesticated red-eared sliders are more prone to suffer from certain nutritional shortfalls as it is often hard to replicate their natural diet in the wild.

This is because wild turtles do not limit their intake of food to any particular kind. They have an omnivorous diet that consists a wide variety of different plants, vegetables, and meat. Many turtles in captivity, on the other hand, are often only given just one or few variety of food, usually commercial pellets. Although many commercial turtle pellets are touted to be rich in multiple nutrients and vitamins, it is simply not enough to make up for a complete nutrition plan, both in terms of quantity and quality.

Metabolic bone disease

Metabolic bone diseases in the most layman terms mean the bone abnormalities of your red-eared slider turtle. Another common name for metabolic bone disease is the Softshell syndrome. But make no mistake, the condition is not only limited to the softening of your turtle’s shell as the name might suggest. Calcium deficiency impacts many other areas of the body, it is just that a softshell happens to be the most obvious signs.

Metabolic bone disease does not describe any particular disorder but is used as a referral to a wide range of conditions to do with the bone.

Often, the most common causes of metabolic bone diseases are dietary issues such as calcium deficiencies, a disproportional ratio between calcium and phosphorus, or inadequate Vitamin D3 for absorption of calcium.

Symptoms of metabolic bone disease

There are several indicators that suggest that your red-eared slider may be suffering from some form of metabolic bone diseases.

Behavioral changes

One of the earlier symptoms of MBD is limping or lameness. The movement pattern differs from what it normally should be, or that they are swimming awkwardly and have difficulty climbing up the platform. They may also display involuntary quivering movements intermittently.

Besides the movement patterns of the red-eared slider, there are also several behavioral changes to look out for. The main one would be the lack of appetite. We all know what greedy eaters turtles are. So when your red-eared slider stops eating or is no longer enthusiastic about its food, you know for sure something is off somewhere. Calcium is not only vital to the building of bones and shell, it is also important for many other functions, such as the contractions of its muscles. A lack of calcium leads to ineffective peristalsis, which is the wave-like contraction of muscles in your gut that pushes the food through your digestive tract. This will cause the turtle’s appetite to be reduced or even anorexia.

Red-eared sliders with metabolic bone diseases are usually also more lethargic and depressed. This may be caused by all the pain the turtle is feeling due to the lack of calcium. I’ve never seen anyone, let alone turtles who suffer from such chronic pain and still appear to be lively.

While the above-described movements and behavioral patterns can be attributed by many things and not just signs of metabolic bone diseases, It is definitely worth taking a closer look when your red-eared slider starts to display any of the symptoms for 2 simple reasons :

  1. MBD or not, there’s definitely something wrong with the turtle.
  2. By the time physical symptoms start to show, it may already have caused some permanent damage to your turtle’s health that is irreversible.

Physical Changes

At the more serious end of the spectrum, turtles suffering from metabolic bone diseases will develop certain physical signs.


More commonly, the shell of the turtle may appear to feel rubbery and softened (Hence the name Softshell syndrome). Another obvious telltale sign would by pyramiding of the turtle’s shell. Pyramiding refers to a shell deformity that is commonly found turtles living in captivity where the shell develops unevenly, causing the scutes to rise resembling a pyramid shape. In even more severe cases, the shell may be deformed or start to rot and crack.


The limbs of the red-eared slider will also become very weak due to the uneven muscle mass resulting from the lack of calcium. Calcium deficiency will also cause the turtle to appear bow-legged. This is due to the weakness of its joints that causes tremendous pain and stress for the turtle.

The claws of red-eared sliders suffering from metabolic bone diseases may also curve outward in an unnatural way.

Head Area

The head of a turtle suffering from MBD may appear to be swollen with hard lumps appearing on various areas.

The overall geometry of a healthy red-eared slider’s head should be symmetric. Any asymmetric or swollen area around the skull is another known symptom of metabolic bone disease.

The beak and jaw area of a healthy turtle should be smooth and firm. Any signs of softened or rubbery jaws may also be another sign of MBD.

Causes of Metabolic Bone Disease in Reptiles

It can be caused by a broad spectrum of disorders. The most common causes are usually a deficiency of minerals such as calcium. However, Higher calcium intake alone is not enough to treat or prevent metabolic bone diseases. It is also essential that your red-eared slider has adequate Vitamin D intake while maintaining a good Calcium to phosphorus ratio.

What is Calcium to phosphorus ratio?

We mentioned that it is vital to maintaining a good Calcium: Phosphorus ratio (Ca:P) in your red-eared slider turtle’s diet. So what is the precise optimum ratio then? Honestly, We don’t know. What we know is that as long as you follow a proper and nutritious dietary plan with different varieties of greens for your red-eared slider, you’d be fine.

The proper diet for your red-eared slider should contain somewhere between 1:1 to 2:1 ratio (2 parts calcium: 1 parts phosphorus).

Can my turtle have too much calcium?

As red-eared slider owners become more aware of the ill effects of calcium deficiency, there has been an increased risk of adding too much calcium to their reptile’s diet. Too much of anything can never be good (with the exception of money). Excessive calcium intake will result in hypercalcemia. Hypercalcemia is a medical condition whereby the calcium level in your red-eared slider’s bloodstream is above normal.

We all know that Calcium is the main building block for bones and shells, but even too much calcium can lead to weakened bones. They can also lead to kidney stones or even kidney failure. Another consideration when it comes to excessive intake would be Hypervitaminosis D. Hypervitaminosis D occurs when you give your red-eared slider too much vitamin D than the recommended level. The negative impact of both conditions is fairly similar.

Treatment of metabolic bone diseases

A red-eared slider that is suffering from metabolic bone disease in the early stages will usually recover with dietary improvements consisting of a rich calcium and vitamin D, and more access to full-spectrum UV light from either a fluorescent lighting or under the sun. For more severe cases where physical traits such as pyramiding of the shell or deformity are visible, the turtle may need calcium and vitamin D injections, medications, therapy and nutritional support.

However, By the time deformity starts to show, some form of permanent damage has already been done to its internal organs that are most probably irreversible.

When it comes to treatment of metabolic bone diseases, prevention is much better than cure

What are the various ways of increasing Calcium & Vitamin D



Red-eared slider turtles are heliothermic species. This meant that they need to be exposed to UVB light In order for them to synthesize Vitamin D3. Dietary means of vitamin D3 are not enough for them as they manufacture Vitamin D3 in their skin. Needless to say, the best source of UV light would, of course, be from the Sun. However, we understand that not everyone may have full-time access to direct sunlight due to various reasons. It could be climatic and seasonal changes, or it could be due to the time schedule. If you have to work during the day, it is simply not feasible to bring your pet turtle our for some sun time if you don’t have a pond in your backyard.

If that is the case, you can always use artificial sources like a UVB fluorescent light as a substitute. But you should always try to bring your turtle out for some fresh air and natural sunlight whenever possible.

Read also…

How to properly set up a basking area for your red-eared slider tank.

What is the best Basking lamp for your red-eared slider turtle?


We have discussed on the relationships between calcium, phosphorus & vitamin D3 and how they impact the turtle’s diet. If you have missed out on that, here’s a quick summary of their relationship in 3 points:


  1. Calcium is important for strong bones, shells, and muscle.
  2. Red-eared slider needs vitamin D3 in order to synthesize the calcium for its body to absorb.
  3. The Calcium intake should not be lower than phosphorus.


Phosphorus is found in most of the foods that turtles eat. Hence, the focus should be placed on the calcium intake.

The vast majority of vitamins and minerals intake for your red-eared slider comes from its diet. Reproducing the natural diet is undoubtedly the best way to keep your red-eared slider a happy and healthy turtle. In the wild, red-eared slider turtles have a vast selection of food depending on seasonal and environmental changes. There isn’t any particular food that is capable of providing for ALL your red-eared slider’s nutritional needs. This is because different food varies in the quality, type, and proportion of the nutrients present. Certain food also has traces of micro-nutrients and minerals that are not found in others. Hence, Variety is one of the main key points for a good dietary plan.

So what is good calcium food for red-eared slider?

There are many different types of food you can offer to your turtle for a healthy and adequate calcium diet. Here are some of the options:

Commercial Pellets

Majority of the commercial pellets sold at your local pet stores contain some calcium for your turtle. A good quality turtle pellets should have a variety of vitamins and minerals necessary for your turtle. You can see the how much calcium, phosphorus and vitamin D the pellet provides by reading the nutritional label at the back.

Turtle pellets are also a very convenient form of food for your turtle. Hence it is the most common and usually the main staple food for most pet red-eared sliders. However, Pellets should never be relied on as the sole source of nutrient for your turtle. Whenever possible, you should always provide your turtle with a wide variety of food to the fulfillment of dietary requirements.

Zoo Med Natural Aquatic Turtle Food

For domesticated red-eared sliders, pellets often make up the largest portion of the turtle’s diet. Hence, the type of pellets that are fed to your turtle is paramount. The Zoo Med turtle pellets are highly regarded to be the top choice among pet owners. Red-eared sliders have different nutritional needs depending on their life stages. Zoo Med is well aware of this and has thoughtfully produced 3 different formulas: Hatchling, Growth & maintenance.

The Hatchling formula has a higher concentration of protein to aid growth in young turtles. Whereas the Growth and Maintenance formulas are tailored to the dietary needs of the turtles at their respective stages.

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Contrary to popular belief that calcium only comes from meat and milk, there are Vegetables that provides a good amount of high-quality calcium. Most vegetables also grant many other health benefits and provide various other minerals apart from calcium. As your red-eared slider turtle grow older and mature, Vegetables and plants should make up the majority portion of their overall diet.

Some examples of vegetables high in calcium are Collard Greens, Kale, Turnip greens.

There is some evidence that Oxalic acid in certain vegetables can hinder the process calcium absorption. Hence, there are many people on the internet that will tell you to avoid spinach like a plague.

We think that it doesn’t really make much sense…

It is true that Spinach contains oxalic acid. However, according to WHfood, Spinach also contains the following nutrients:

Vitamin K

Vitamin A






Vitamin B2

Vitamin B6


Vitamin C

Vitamin E



Vitamin B1





Omega-3 fats

Vitamin B3


Pantothenic acid

Besides that, if your turtle is getting its required intake of Vitamin D3, which is the key component to metabolize calcium, there isn’t really any need to be concerned about the oxalates in spinach.

Live Feeds

Meats & live feeds are very rich sources of calcium. Vitamin D3 can found in the liver oils of prey fishes. Crustaceans such as shrimps and krill with the shell are an excellent calcium source. However, as much as meat is a rich source of calcium, it also has very high amount of protein and phosphorus. We have mentioned several times on calcium x phosphorus ratio in this article. Note that it is much easier to overload on phosphorus than calcium. So you should try to opt for lower phosphorus food as much as possible. It is still OK to give your turtle live feed and meat on occasional basis thou.

Feeding Goldfish to your red-eared sliders is inadvisable as the fat content in goldfishes is too high and they don’t really offer much nutritional value.

Also, while live shrimps with shell offer great calcium value, commercially dried shrimps should be avoided as they might start to avoid other food if they are given dried shrimps too often.

Supplements & Multivitamins

Even with a full spectrum of a nutritious dietary plan and adequate sun time for Calcium & Vitamin D, additional nutritional supplements for your red-eared slider such as multivitamins and calcium should still be incorporated into your pet turtle’s food every now and then.

It is almost impossible for pet keepers to completely replicate the natural living condition of a red-eared slider, both in terms of diet and natural habitat. So we have to ensure that they are able to receive all the nutrients they need under captivity.

Luckily for us, vitamins & supplements for red-eared sliders are easily available. You can find them in all decent pet-store, or just look online and have them delivered to you the next day!

Rep-Cal Phosphorous-Free Calcium Powder

One way of adding calcium to your red-eared slider’s diet would be adding calcium into the daily diet. The Rep-Cal calcium power contains 100% natural calcium carbonate and it is phosphorous free. It can be easily mixed with vegetables or fruits as an addition.

Rep-Cal calcium power is formulated to ensure excellent growth and health for your turtle by providing a complete and well-balanced nutrition. The Rep-cal calcium power does not contain any Vitamin D3 as it is meant for pets that have access to sunlight. So if you are looking for calcium supplement with Vitamin D3 inclusive, you can check out the Zoo Med Calcium With Vitamin D3


Zoo Med Calcium With Vitamin D3 Reptile Food

The Zoomed calcium supplement is also a great alternative to add calcium and Vitamin D3 to your turtle’s diet. It is an ultra fine Precipitated Calcium Carbonate Supplement. Like the Rep-cal, this is also phosphorus-free. There is no need for phosphorus supplements as it is found in many of the turtle’s diet. Sprinkle on mealworms and vegetables and it easily coats almost every food that is not already dried.


Another great way of adding more calcium to your turtle’s diet is to feed them cuttlebone. Cuttlebones are often used by bird owners as alternative calcium supplements for birds and as a beak trimmer. So, you should probably find one in the bird section in your local pet shop. A cuttlebone is not really a bone, instead. It is the internal shell of a Cuttlefish. Cuttlebones are lightweight, chalky object that is approximately 85% calcium.

While cuttlebone provides very high calcium content, the main challenge here is getting your red-eared slider to actually be interested in eating the cuttlebone.

Slow-release Calcium Blocks

Calcium blocks are white little chalk-like chess piece that is made up of main calcium. It is placed into the turtle tank to increase the calcium level of the water. This can help to promote healthier shell development for your red-eared slider.