The diet Saskia is recommending (the so called ph : ca or phosphorus : calcium ratio diet) has been making the rounds for about a decade now. The problem is that you have to get that ratio exactly right because you are otherwise feeding a high calcium diet with the obvious consquences.
My issues with it are:
- Any ph : ca vegetable diet covers only about 10-20 % of the daily food intake but seems to totally ignore all the other factors that are most definitely in play; if more in some countries than others. Any US-based charts are more likely to fail in the UK in our forum experience.
- A lot of calcium can actually come in hard water; more than with veg. But water hardness differs massively around the world, as does individual water intake in guinea pigs. This is crucial, especially in a mostly hard water country like the UK (which is one of the worst in this respect). The US for instance is largely a soft water country. Even throughout the UK we have areas that struggle more with bladder stones than others.
Bottled water brands differ in calcium content and they come with long term plastic consumption/waste concerns; you will need to find a low calcium brand, which is not easy because most brands are high calcium.
While filtered water is generally making a noticeable difference when it comes to the development of stones, it is not as effective in filtering out all calcium. For guinea pigs you struggle with repeated stone formation (i.e. factors in the complex calcium absorption process that you cannot control with diet alone), bottled low calcium water is the better option; for most others, filtered water will usually do the trick.
- Hay is the largest food group and there are varieties of hay that differ in calcium content, so a guinea pig on meadow hay will eat some more calcium than timothy hay (it is not huge amounts more, but it can play into the overall balance when it is close to the tipping point). The same goes for any dry forage and speciality treat hays; they are often higher in calcium due to the evaporated water. Hay intake between piggies and from day to day can also vary quite noticeably.
- Pellets also can have very differing calcium content and there needs to be a chart for working out a standard in terms of calcium content vs. amount to feed. The phosphorus content in the pellets (i.e. the ph : ca ratio) is another big question.
Next to water, pellets are the next largest contributor of calcium in the diet. Weight for weight, the calcium content in even no added calcium pellets is noticeably higher than that in the veg highest in calcium, kale.
A good number of the long standing forum members have tried the ca : ph diet when it came on the scene big time first. With one notable exception, we have all made negative experiences. This is why we have withdrawn the ph : ca thread and no longer recommend it.
NOT because the ph : ca diet is essentially wrong - when you get it right, it actually works - but because it is so very easy to get it just wrong and the consquences can be costly.
When we have one person saying that it works for them and ten others on here that it hasn't worked out, then are some obvious issues that have not been factored in and may never be satisfactorily resolved. As long as there is no reliable chart to work out the
overall calcium intake : phosphorus ratio irrespective of where you are in the world, we won't back it as a forum because the safety of any piggy on here is paramount for us. I may also add that in many countries, even European ones, getting hold of good pellets, low calcium water (most bottled water is high in calcium) or timothy hay can be rather difficult.
PS: On a strictly personal basis, two extra bladder stone ops in short succession just a few weeks into the ph : ca ratio diet where a bit in the way of a rather expensive failed diet experiment as far as I am concerned...
PS2: That is also why I am clearly saying at the start of our diet thread that what we recommend (i.e. a low to moderate calcium diet) may not necessarily be the best, but we can at least say that it works on the whole and that the occurrance of bladder stones in our regular UK members has come down massively on it. In the eight years since my failed diet experiment, I have only ever had one more bladder stone (in the wake of the Covid Lockdowns and balanced veg access problems) in the more than 50 piggies that have lived here since. (updated May 2022)
In any case, our moderate calcium sample diet is what has stood the test of time here in the UK when it comes to long term experiences with bladder and kidney stones; calcium and mineral content vary across the country so you have to work out for yourself how much higher or lower in calcium you may want to go until you have found your personal ideal balance. You can never eliminate the stones that come from a genetic disposition/something going wrong with calcium absorption process.
(PS: The slice of greens we recommend in our sample diet is a less calcium high relative of kale but you are welcome to replace it with kale if you live in a soft water area.)
For any piggies with known bladder problems a low (but NOT NO) calcium diet is always the safer option in any case as factoring in a likely genetic disposition or a problem with the calcium absorption is not easy...
PS3: Generally a grain-free and low sugar diet (no carrots, tomato or fruit!) should be observed for piggies with long term health issues (diabetes, digestive, urinary tract etc.) - but that then also goes for recommending feeding porridge oats (grain!) and carrots (high sugar) to help keep up the weight in frailer piggies, so you can see the problems you quickly get into...
For healthy piggies a low grain and low sugar diet is acceptable, i.e. if you can only get grain based pellets (alfalfa by the way is a legume and not a member of the grass family), then to may want to feed a bit less. Grain-free pellets have only been around for the last few years. Ten years ago the calcium content in pretty much all commercially available pellet brands was a lot higher than it is today and they were mostly alfalfa based.
These measures take care of the oxalates that play a role in the formation of stones and contribute to a reduction in the formation of stones that can be controlled by diet.
Basically, the ph : ca ratio diet would be great if you could get it to work safely for everybody everywhere, but there is still a massive practical BUT in the actual implementation...
I'll go and check out the comment section now.
This one you posted is more of her clarification on her side. 
