Wow, 15000l cistern is not even 4,000 gallons of water. It's a pretty small system, at least by U.S. standards.
You might want to consider using a home made buffer recipe as it is much cheaper using baking soda, epsom salts and aquarium salt to raise your pH, KH and GH. You will also get better control over your water parameters once you figure out the ingredient ratio you need for your low pH rainwater. And once you determine the correct ratios, you'll have no problems with maintaining good water quality. You will need to do an internet search to get the recipe for making your own aquarium buffer at home.
While following the above recommendations for making your own buffer won't help your immediate problems with ammonia and nitrite, it will help you get your cycling problem under control. In the mean time, the only thing you can do is to increase your daily water changes to help reduce the ammonia, nitrite and nitrate in the tank and continue to add Prime and neutral regulator to the water change water.
I also suggest that you tell your wife that if the cistern runs out of rainwater and she has scheduled a delivery of town water, that she post a very large note on the aquarium informing you of that fact.
Since you will be doing large water changes on your tanks due to the fish stocking levels and cycling problems, I suggest you look into buying a powdered dechlorinating product like Safe or Chlor-am-X. It will be much cheaper than using the liquid Prime. It works the same but you will be using less product to achieve the same results at a fraction of the cost.
If you are handy at DIY projects, you might want to consider installing a manual or automatic drip system on your 180G tank. You would also have to come up with some type of auto dosing system to add buffers to the tank to maintain the correct pH, GH and KH levels. Check out the stickies in the the DIY projects for some suggestions.
You might want to consider using a home made buffer recipe as it is much cheaper using baking soda, epsom salts and aquarium salt to raise your pH, KH and GH. You will also get better control over your water parameters once you figure out the ingredient ratio you need for your low pH rainwater. And once you determine the correct ratios, you'll have no problems with maintaining good water quality. You will need to do an internet search to get the recipe for making your own aquarium buffer at home.
While following the above recommendations for making your own buffer won't help your immediate problems with ammonia and nitrite, it will help you get your cycling problem under control. In the mean time, the only thing you can do is to increase your daily water changes to help reduce the ammonia, nitrite and nitrate in the tank and continue to add Prime and neutral regulator to the water change water.
I also suggest that you tell your wife that if the cistern runs out of rainwater and she has scheduled a delivery of town water, that she post a very large note on the aquarium informing you of that fact.
Since you will be doing large water changes on your tanks due to the fish stocking levels and cycling problems, I suggest you look into buying a powdered dechlorinating product like Safe or Chlor-am-X. It will be much cheaper than using the liquid Prime. It works the same but you will be using less product to achieve the same results at a fraction of the cost.
If you are handy at DIY projects, you might want to consider installing a manual or automatic drip system on your 180G tank. You would also have to come up with some type of auto dosing system to add buffers to the tank to maintain the correct pH, GH and KH levels. Check out the stickies in the the DIY projects for some suggestions.