It‘s an African Cichlid tank and needs to come up from 6.2 to 7.6.
Mu-metal is a nickel-iron alloy (75% nickel, 15% iron, plus copper and molybdenum) that has very high magnetic permeability. Permeability is represented by μ. The high permeability makes mu-metal very effective at screening static or low-frequency magnetic fields, which cannot be attenuated by other methods. It is very expensive to manufacture.
Especially in a cichlid tank. Any fish will die from pH shock if you change the pH levels to quickly. You didn’t mention any specifics about your tank set up and if you are or aren’t new to cichlid care so forgive me if you know any of the following. You should be using Dolomite as a substrate, not standard aquarium gravel. It will help keep the pH in the tank stable once you get it where you need it to be. Dolomite is readily available in just about any neighborhood fish store. There is an alternate choice called Eco-Complete which actually does a better job, but I’ve not found it to be readily available in my neck of the woods. The proper chemical to use for adjusting the pH is sold as a cichlid buffer. How much you will use each time is dependant on the which lake your cichlids are from (Malawi, Tanganyika, etc). The recommended dosages can be found on the label. Give your tank 24-48 hours before doing a post-buffer test for an accurate reading. A couple of days in low pH won’t kill them. Too rapid a change will. You should also be adding cichlid salt at each water change. Remember: only add buffers and chemicals with water changes NOT when topping or for evaporation loss. I found it easier to keep my tank stable with a weekly change of 25%. I can sometimes stretch it to two weeks but cichlids need very clean water to thrive. Additionally, large changes (50% or so) can instigate breeding behavior.
Adding this to the water will increase the PH value of the water. Be very careful not to use too much. This will only be temporary, and more will need to be added to maintain this higher PH. Another way to raise the PH is to add limestone rocks to your decorations in the aquarium. You will not have control over how much this changes the PH, but you will not have to add more rocks routinely like the baking soda. I hope this helps.
The only way to block a magnet that I know of is with space, and dense material, like concrete or non-magnetic metal like aluminium. Since magnetizm can pass through most 'solid' objects, you need distance to reduce the power of the magnet. Now, you can also counter it with another magnetic field of opposed polarity (Negaive/Positive, you know). But you'd ahve to do all kinds of crazy math to know exactly how much of an opposing chrage to generate.
i wouldnt use any chemicals, unless they were ment for that, try going to your pet store and asking for water pills that raise PH, if u insist then take the fish out of the tank and put in a little bit of milk then wait about an hour before putting them back in but this is risky and not a good idea.
