Cloud tank after feeding

Fish problem is that yesterday I found two dead guppies in the tank and I'm now worried about there health

 

Yeah ... though call to make. See if they are better in the other tank then rather.

 

I lost myIce blue male and my Yellow Micraffe male which is quite a nock.

 

It sounds like it could be some kind of spike of either bacteria or ammonia.
That it happens straight after feeding seems to indicate that the water is reacting to the introduction of the food.
How soon after feeding does the water turn cloudy after feeding?

I was taught that you don't disturb the substrate, apart from vacuuming it.
Removing everything from the tank and then swishing and swirling the substrate almost sounds as though you are removing most of the gunk from the substrate, which is where the beneficial bacteria breeds.
When I siphon my tank, I just press the vacuum into the substrate, and let if suck up any dirt that way.
There is enough movement that there isn't a gas build-up, the substrate gets cleaned sufficiently, and the tanks remain healthy.

If the filter has been running for a few weeks, there should be sufficient build up of bacteria.
Perhaps use a bacterial seeding agent like Seachem Stability again for a few days at the recommended dosages, and see what happens.

The fact that fish are dying indicates that the problem is serious, and the only issue I can think of is the water parameters, caused by a spike in either the ammonia or bacteria.

 

@Pezulu At first I thought iy was ok since my water test came back rather normal except for the low ph.

It turns cloudy about an half an hour to an hour after feeding?

I have already removed everything from the tanks and I'm going to keep my fish in the 200l until my tanks are cycled again. I'm really confused because I feed my 200l exactly the same food with no issues at all. I really believe that the filter has something to do with it since my second tank only started doing it too after I added the internal filter to the second tank. If I have to I would rather replace the filter to solve the problem. But I have honestly come to the conclusion that the filter has something to do with the problem.

In the four years I have had fish this as never been a problem since I never do the filter and the gravel in the same week since I'm aware of the bacteria that also grows in the gravel and not just in the filter.

 

I've had no incidents and also more stable water parameters since I switched to barebottom

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My second tank is bare bottom, and only got this problem after I added the filter to the tank.
I have now cleaned both tanks and rinsed, sterilized and re sinsed both tanks and all equipment used in the tanks. My 2ft tank is already fulled and started to cycle added a deformed guppy and some fish food with no issues. My second tank is cleaned and ready to have water added.

The sand of my 2ft tank really smelled off when I washed it. Took me most 2 hours to get it ready for my tank but I'm happy since the last rinse the water was completely clear.

 

Yeah your nose will tell you the truth. Tanks if planted should have a green grassy smell - then all is good.